## Posts tagged ‘puzzle’

### Our Library’s Summer Math Contest

Every summer, our local library runs a contest called *The Great Big Brain Game*. Young patrons who solve all of the weekly puzzles receive a prize. The second puzzle for Summer 2017 looked like a typical math competition problem:

Last weekend, the weather was perfect, so you decided to go to Cherry Hill Park. When you got there, you saw that half of Falls Church was at the park, too! In addition to all the people on the playground, there were a total of 13 kids riding bicycles and tricycles. If the total number of wheels was 30, how many tricycles were there?

First, some comments about the problem.

- I dislike using “you” in math problems. I believe it’s a turn-off to students who can’t see themselves in the situation described. There are enough reasons that kids don’t like math. Why give them another reason to shut down by telling them that they went somewhere they didn’t want to go or that they did something they didn’t want to do?
- Word problems are not real-world just because they use a local context, and this one is no exception. This problem attempts to show an application for a system of linear equations, but true real-world problems don’t have all the information neatly packaged like this.
- Wouldn’t the person posing this problem already have access to the information they seek? That is, if she counted the number of kids riding bikes and the total number of wheels, couldn’t she have just counted the number of bicycles and tricycles instead? It has always struck me as strange when the (implied) narrator of a math problem wants you to figure out something they already know.

All that said, this was meant to be a fun puzzle for a summer contest, and I don’t mean to scold the library. I don’t know that I’d use this puzzle in a classroom — at least, not presented exactly like this — but I love that kids in my town have an opportunity to do some math in June, July, and August.

Now, I’ll offer some comments on the solution. In particular, the solution provided by the library was different than the method used by one of my sons. Here’s what the library did:

Imagine that all 13 kids were on bicycles with 2 wheels. That would be a total of 26 wheels. But since 30 wheels are needed, there are 4 extra wheels. If you add each of those extra wheels to a bicycle, that’ll create 4 tricycles, leaving 9 bicycles. So, there must have been 4 tricycles at Cherry Hill Park.

And here’s what my son did:

If you can’t see what he wrote, he created a system of two equations and then solved it:

2a + 3b = 30

a + b = 13a + 2b = 17

13 – b + 2b = 17

b = 42a + 12 = 30

2a = 18

a = 9

That’s all well and good. In fact, it’s perfect if you want to assess my son’s ability to translate a problem and solve a system of equations. But I have to admit, I was a little disappointed. What bums me out is that he went straight to a symbolic algorithm instead of considering alternatives.

I think I know the reason for this. This past year, my son was in a pull-out math program, in which he studied math with someone other than his regular classroom teacher. In this special class, the teacher focused on preparing him to take Algebra II in sixth grade when he enters middle school. Consequently, students in the pull-out class spent the past year learning basic algebra. My fear is that they focused almost exclusively on symbolic manipulation and, as my former boss liked to say, “Algebra teachers are too symbol-minded.”

A key trait of effective problem solvers is flexibility. That type of flexibility comes from solving many problems and filling your toolbox with a variety of strategies. My worry — and this isn’t just a concern for my son, but for every math student in the country — is that students learn algorithms at the expense of more useful problem-solving heuristics. What happens when my son is presented with a problem that can’t be translated into a system of linear equations? Will he know what to do when he doesn’t know what to do?

The previous pull-out teacher said that when she presented my sons with problems that they didn’t know how to solve, their eyes would light up. They liked the challenge of doing something they hadn’t done before. I’m hopeful that this enthusiasm isn’t lost as they proceed to higher levels of mathematics.

### Friday Word Puzzle

Sometimes, a small word is contained in a longer word. For example, you can see the three-letter word *rid* tucked nicely inside *F riday* in the title for this post, and

*zip*can be found in the middle of

*mar*.

**zip**anSome folks have told me that the following word-in-a-word is particularly appropriate for this blog…

…since my puns put the UGH in LAUGHTER.

Words within words are the basis of today’s puzzle.

Complete each of the nine words below by placing a three-letter word in the blank. The three-letter words that you use all belong to the same category. But there is a tenth three-letter word from the same category that is not used below. What is the category, and what is the missing word?

- OB _ _ _ D
- C _ _ _ PY
- M _ _ _ OT
- PH _ _ _ M
- H _ _ _ SE
- VE _ _ _ D
- CA _ _ _ OU
- EL _ _ _ SE
- LE _ _ _ E

When I started to create this puzzle, I was hoping to give you a similar list in which a short math word was found in a longer word. I found several, but they seem pretty darn hard, and the missing words aren’t always obviously mathy. But for fun, you can try your hand at these, too…

- D _ _ _ Y
- AS _ _ _ E
- SE _ _ _ H
- BU _ _ _ _ SS
- EL _ _ _ _ TH
- C _ _ _ _ RA
- RU _ _ _ _ NT
- SH _ _ _ _ BLE
- BRA _ _ _ _ ILD
- HU _ _ _ _ D
- PR _ _ _ _ _ IFY
- RE _ _ _ _ NT
- WA _ _ _ _ ELON
- DE _ _ _ _ OR
- HO _ _ _ _ SS
- H _ _ _ _ HOG
- IM _ _ _ _ ST

ANSWERS

- OB eye D
- C hip PY
- M arm OT
- PH leg M
- H ear SE
- VE toe D
- CA rib OU
- EL lip SE
- LE gum E

The three-letter words are all parts of the body. The tenth word in that category is *jaw*, which never appears in the interior of a longer word (only at the beginning or end, such as * jawbone* or

*lock*).

**jaw**- D add Y
- AS sum E
- SE arc H
- BU sine SS
- EL even TH
- C hole RA
- RU dime NT
- SH area BLE
- BRA inch ILD
- HU more D
- PR equal IFY
- RE side NT
- WA term ELON
- DE mean OR
- HO line SS
- H edge HOG
- IM mode ST

### Dos Equis XX Math Puzzles

No, the title of this post does not refer to the beer. Though it may be the most interesting blog post in the world.

It refers to the date, 10/10, which — at least this year — is the second day of National Metric Week. It would also be written in Roman numerals as X/X, hence the title of this post.

For today, I have not one, not *two*, but **three** puzzles for you. I’m providing them to you well in advance of October 10, though, in case you’re one of those clever types who wants to use these puzzles on the actual date… this will give you time to plan.

The first is a garden-variety math problem based on the date (including the year).

Today is 10/10/16. What is the area of a triangle whose three sides measure 10 cm, 10 cm, and 16 cm?

Hint:A triangle appearing in an analogous problem exactly four years ago would have had the same area.

The next two puzzles may be a little more fun for the less mathy among us — though I’m not sure that any such people read this blog.

Create a list of words, the first with 2 letters, the second with 3 letters, and so on, continuing as long as you can, where each word ends with the letter X. Scoring is triangular: Add the number of letters in all the words that you create until your first omission. For instance, if you got words with 2, 3, 4, 5, and 8 letters, then your score would be 2 + 3 + 4 + 5 = 14; you wouldn’t get credit for the 8-letter word since you hadn’t found any 6- or 7-letter words.

2 letters: _________________________

3 letters: _________________________

4 letters: _________________________

5 letters: _________________________

6 letters: _________________________

7 letters: _________________________

8 letters: _________________________

9 letters: _________________________

10 letters: _________________________

11 letters: _________________________

12 letters: _________________________

13 letters: _________________________

14 letters: _________________________

Note: There are answer blanks above for words up to 14 letters, because — you guessed it — the longest English word that ends with an X contains 14 letters.

The third and final puzzle is a variation on the second.

How many words can you think of that contain the letter X

twice? (Zoiks!) Scoring: Ten points for the first one, and a bazillion points for each one thereafter — this is hard! Good luck!

If you’re in desperate need of help, you can access **my list of words for both puzzles** — of which I’m fairly proud, since my list of words that end in X include math words for 2 through 10 letters — or do a search at www.morewords.com.

### AWOKK, Day 7: KenKen Puzzle for 2016

Good day, and welcome to Day 7 of the **A Week of KenKen** series. If you’ve stumbled onto this page randomly, you should definitely check out some of the fun we’ve had previously…

- Day 1: Introduction
- Day 2: The KENtathlon
- Day 3: KenKen Times
- Day 4: My KenKen Puzzles
- Day 5: Harold Reiter’s Puzzles
- Day 6: KenKen Glossary

Well, here it is, September 25, a mere 269 days into the year, and I am only now presenting you with a KenKen puzzle based on the year. I suppose I can take some solace in the fact that I’m presenting the following 2016 KenKen puzzle before the year is over. Little victories.

You might note that the puzzle has the following attributes:

- The numbers 2, 0, 1, and 6 are featured prominently as individual cells.
- Every target number uses (some combination of) the digits 2, 0, 1, and 6.
- There are two large cages — one in the shape of a 1, the other in the shape of a 6 — each with a product of 2016.

This puzzle follows the standard rules of KenKen, but there is one major exception: although it is an 8 × 8 puzzle, **instead of using the digits 1‑8, it uses 0‑7**.

If you’re stuck, just fill in the squares randomly. There are only 108,776,032,459,082,956,800 different Latin squares of size 8 × 8, and your chances of guessing correctly are even better since 4 cells are already filled in.

As it typical of all puzzles presented on this blog, I am not posting the solution. At least, not yet. Maybe someday. If you beg. Or send me money. But not today.

### AWOKK, Day 6: KenKen Glossary

KENgratulations! You’ve made it to Day 6 of MJ4MF’s **A Week of KenKen** series. If you happened to miss any of the fun we’ve had previously…

- Day 1: Introduction
- Day 2: The KENtathlon
- Day 3: KenKen Times
- Day 4: My KenKen Puzzles
- Day 5: Harold Reiter’s Puzzles

Robert F. Fuhrer is a toy inventor with a knack for coming up with creative names, including Crocodile Dentist, Gator Golf, T.H.I.N.G.S. (Totally Hilarious, Incredibly Neat Games of Skill), Rumble Bugs, Missile Toe (literally, a rocket in the shape of a toe), and many others. As the president of Nextoy, LLC, which holds the registered trademark for KenKen^{®}, Bob now uses his creative naming abilities for the appellations of KenKen-related products.

The word that started this post, KENgratulations, is just one of his many linguistic creations. I rather like the term he coined to describe the computer application that randomly generates KenKen puzzles.

**KEN·****er·****a·****tor** *n.* the “machine” (computer application) used to automatically generate KenKen puzzles

*Quick! We need more 6 × 6 puzzles. Crank up the Kenerator!*

The name conjures images of a machine from Willy Wonka.

Oompa, loompa, doom-pa-dee-do,

I’ve got a perfect puzzle for you…

Numbers and operations go in, puzzles come out.

Bob can also take credit for the following:

**KEN****·cil** *n.* a pencil used to solve KenKen puzzles

*I prefer kencils rather than pens when solving KenKen puzzles. *

**KEN****·grat·****u·****la·****tions** *n.* an expression of praise for solving a KenKen puzzle

**Kengratulations** for solving that puzzle in less than 7 years!

**KEN****·thu****·si****·ast** *n.* someone who likes to solve KenKen puzzles

*Most Kenthusiasts solve more than one KenKen puzzle a day.*

There’s no doubt, Bob is good. But as you saw in a previous post, I’ve got a knack for coining terms, too…

**KEN·tath·lon** *n.* competition involving multiple KenKen events

*I complete a Kentathlon consisting of a 4 × 4, 5 × 5, and 6 × 6 puzzle every morning.*

**e·go·KEN·tric** *adj.* a person who thinks that they are better than others at solving KenKen puzzles

*He’s completely egokentric, even though he’s never won a KenKen tournament.*

**KEN·tral of·fice** *n.* where KenKen puzzles are made

*The Kenerator resides in the kentral office.*

**KEN·te·nar·i·an** *n.* person who has solved 100+ KenKen puzzles

*He became instantly addicted to KenKen puzzles; he became a kentenarian in less than 3 weeks.*

**su·per·KEN·te·nar·i·an** *n.* person who has solved 100+ KenKen puzzles *in one day*

*She became a superkentenarian by completing all the puzzles in Ferocious KenKen on Saturday.
*

**KEN·ta·gon** *n.* the arena in which KenKen tournaments take place (analogous to the Octagon, the eight-sided chain-link enclosure used for Ultimate Fighting Championship matches, though usually less violent)

*Enter the kentagon, prepare to solve!*

**KEN·o·pause** *n.* the period in a puzzle solver’s life when KenKen ceases to be fun

*Kenthusiasts who have entered kenopause usually solve fewer than one puzzle a day, on average.*

**KEN·i·ten·tia·ry** *n.* where KenKen solvers are locked up if they’re caught cheating (*syn* **prism**)

*If you copy off your neighbor at a KenKen tournament, you’ll be sent to the kenitentiary.*

**KEN·al·ty** *n.* a disadvantage imposed on a puzzle solver at a tournament for an infringement of the rules

*He was given a 15-second kenalty for “using a kencil in an unsafe manner.” *

**KEN·ais·sance** *n.* the period from roughly 2008 to 2010 when KenKen puzzles experienced tremendous growth in popularity, likely the result of publication in *The* *Times* (London), the *NY Times*, and other newspapers

*Harold Reiter’s interest in KenKen started long before the Kenaissance.*

**KEN·der·foot, ***n.* an amateur; someone who has solved only a few KenKen puzzles

*He’s such a kenderfoot; he doesn’t even know the X-wing strategy!*

**KEN·den·cies** n. the habits of a KenKen solver; analogous to a “tell” in poker

*He has a kendency to complete all of the addition cages before attempting any subtraction cage.*

**hy·per·KEN·ti·late** *n.* to breathe heavily while solving a puzzle (usu., a result of having difficulty)

*At the 2013 KenKen International Championship, she started to hyperkentilate when she had trouble with a difficult 6 × 6 puzzle.*

### AWOKK, Day 5: Harold Reiter’s Puzzles

You’ve made it! Today is Day 5 in MJ4MF’s **A Week of KenKen** series. In case you missed the fun we’ve had previously…

- Day 1: Introduction
- Day 2: The KENtathlon
- Day 3: KenKen Times
- Day 4: My KenKen Puzzles

Like Thomas Snyder, Harold Reiter believes that human-generated KenKen puzzles are superior to those created by computer. But Harold pushes the envelope by developing variations on KenKen that include Primal KenKen, 3-D KenKen, *n* × *n* KenKen puzzles that use numbers other than 1‑*n*, and Clueless KenKen — which contain no clues and, contrary to popular belief, were not invented by Cher Horowitz. Recently, in fact, he sent me a No-Op KenKen puzzle that used the floor function.

The following standard KenKen puzzle is one of Harold’s “Big Letter” puzzles. One of the cages forms a capital E, and he made this puzzle for a friend whose name began with — wait for it — the letter E.

No-Op KenKen Puzzles have target numbers in the cages but no operations. All the typical rules of KenKen apply, but it’ll take a little more thought to determine which operation is needed in each cage. The following is Harold’s “No-Op 12” puzzle.

And the piece de resistance of Harold’s creations — though he says the idea for this one actually came from his daughter, Ashley — is the following 3‑D KenKen. Here are Harold’s instructions for this puzzle:

In the puzzle below, there are 48 lines. Each must contain exactly one of the digits 1, 2, 3, and 4. The 16 cages are identified by letters. Each cage is either additive or multiplicative, and the target number for every cage is 12 — meaning that the numbers in the cells of every cage either add or multiply to give 12. Ken you solve it?

This one might need a little more explanation. The four layers of the puzzle work together; for instance, the two A’s on the top layer and the two A’s on the second layer form a four-number cage with a target number of 12. Similarly, the four G’s on the second layer and the lone G in the third layer form a five-number cage with a target number of 12. All standard KenKen rules apply and are extended to three dimensions — no repeat of a digit in any row, column, or tube vector.

I prefer this presentation of the puzzle, which looks like a 3‑D tic-tac-toe board:

But Harold’s presentation of it gives you a blank version side-by-side with the original, so you have a place to record your work:

The KenKen world is indebted to Harold for creating interesting puzzles *and* for sharing them with a new generation of students at his local math events.

For more of Harold’s puzzles, and for suggestions on how to create your own, check out KenKen, Thinking Globally.

### AWOKK, Day 3: KenKen Times

Today is Day 3 in MJ4MF’s **A Week of KenKen** series. In case you missed the fun we’ve had previously…

- Day 1: Introduction
- Day 2: The KENtathlon

Yesterday, I introduced you to the **KENtathlon**.

While completing a KENtathlon, my goal is to complete a 6 × 6 puzzle in less than 2 minutes; a 5 × 5 puzzle in less than 1 minute; and a 4 × 4 puzzle in less than 20 seconds. Even though the sum of those times for all three puzzles is 3 minutes, 20 seconds, my goal is a combined time of 3 minutes. It’s good to have goals.

Puzzle Size |
Goal Time |
Personal Best |

4 × 4 | 0:20 | 0:12 |

5 × 5 | 1:00 | 0:27 |

6 × 6 | 2:00 | 1:29 |

KENtathlon | 3:00 | 2:32 |

I don’t always perform well enough to meet those goals. And when I don’t, I repeat the same size puzzle again… and again… and again… for as many attempts as it takes to complete each puzzle in the allotted time. And when I’ve met the time goal for each puzzle individually, if the combined time isn’t satisfactory, then I start the whole thing over.

To say that I’m slightly obsessive would be like saying that the Pope is a little bit Catholic.

As you may have noticed in the table, I once finished a 4 × 4 puzzle in 12 seconds. The key word there is **once**. The stars were in alignment that day — it was an easy puzzle, and the dexterity of my thumbs and fingers was at an all-time high. Though I’ve attained 13 a handful of times, I’ve never replicated that 12-second feat.

That said, I regularly complete 4 × 4 puzzles in 14 or 15 seconds. With that being the case, you have to wonder if the 20-second goal is really a challenge. And what about the goal times for 5 × 5 and 6 × 6 puzzles?

Admittedly, my time goals are arbitrary, though not random. When I chose those goals, I had completed enough KenKen puzzles that I intuitively knew what felt right. Still, it wasn’t based on hard data… and if you’ve read this blog long enough, you know that that bothered me. A lot.

But what’s a boy to do?

I suppose a well-adjusted human might do nothing, think it’s not worth the trouble, and just let the whole thing go. But an obsessive numbers guy? Well, he’d painstakingly solve 132 KenKen puzzles, collect data on the amount of time each one took to complete, meticulously record the data in an Excel spreadsheet, and perform a thorough analysis. You may think that undertaking such a project is ludicrous; but to me, it was absolutely essential.

The graph below shows the results. The circular dots represent my median time for each puzzle size, and the square dots represent the upper and lower quartiles. For instance, the median time for 6 × 6 puzzles was 217 seconds, while the interquartile range for 6 × 6 puzzles extended from 163 to 284 seconds.

What this reveals is that my intuition wasn’t perfect, but not bad.

- I completed
**49% of 4 × 4 puzzles**in less than the goal time of 20 seconds. - I completed
**58% of 5 × 5 puzzles**in less than the goal time of 1 minute. - But, I completed
**only 14% of 6 × 6 puzzles**in less than the goal time of 2 minutes.

Further analysis revealed that I completed 40% of the 6×6 puzzles under 3 minutes, and that seems a bit more reasonable, so **my new goal time for 6 × 6 puzzles is 3 minutes**.

Now, I know you thought this analysis was completely unnecessary, but the proof is in the pudding. The results were invaluable. By considering the data, interpreting the results, and revising my goal time for 6 × 6 puzzles, the probability that I can now complete each size puzzle in the allotted time on the first or second try has increased from 16% to 39%. Or said another way, Remy’s morning walks now last an average of just 15 minutes, whereas some of them used to take an hour-and-a-half.