NPR Puzzle Combinations
During yesterday’s NPR Sunday Puzzle, puzzlemaster Will Shortz presented the following challenge:
I’m going to give you some five-letter words. For each one, change the middle letter to two new letters to get a familiar six-letter word. For example, if I said FROND, F-R-O-N-D, you’d say FRIEND, because you’d change the O in the middle to I-E.
He then presented these nine words:
For those of you who don’t know who Will Shortz is, you have something in common with detective Jake Peralta from Brooklyn Nine-Nine:
The puzzle was fun. But what was more fun was the conversation that our family had about it. After the third word, Alex announced, “This shouldn’t be that hard. There are only 676 possible combinations.”
What he meant is that there are 26 × 26 = 676 possible two-letter combinations, which is true.
He continued, “But you can probably stop at 675, because Z-Z is pretty unlikely.”
I smiled. He had chosen to exclude Z-Z but not Q-K or J-X or V-P.
Yet his statement struck me as a challenge. Is there a five-letter word where the middle letter could be replaced by Z-Z to make a six-letter word? Indeed, there are several:
- BUSED or BUSES
- CONED or CONES
- FUMED or FUMES
- RAVED or RAVES
- ROVED or ROVER or ROVES
- WINED or WINES
None of them are perfect, though, because Z-Z is not a unique answer. For instance, ROVER could become ROBBER, ROCKER, ROMPER, ROSTER, or ROUTER, and most puzzle solvers would surely think of one of those words before arriving at ROZZER (British slang for a police officer).
From the list above, the best option is probably GUILE, for two reasons. First, stumbling upon GUZZLE as the answer seems at least as likely as the alternatives GUGGLE, GURGLE, and GUTTLE. Second, the five-letter hint has only one syllable, but the answer has two, and such a shift makes the puzzle just a little more difficult.
But while Alex had reduced the field of possibilities to 675, the truth is that the number was even lower. The puzzle states that one letter should be “changed to two new letters,” which implies that there are only 25 × 25 = 625 possibilities. Although that cuts the number by 7.5%, it doesn’t help much… no one wants to check all of them one-by-one to find the answer.
When Will Shortz presented DEITY, the on-air contestant was stumped. So Will provided some help:
I’ll give you a tiny, tiny hint. The two letters are consonant, vowel.
Alex scrunched up his brow. “That’s not much of a hint,” he declared.
Ah, but it is — if you’re using brute force. To check every possibility, this reduces the number from 625 to just 21 × 5 = 105, which is an 80% reduction.
Still, Alex is correct. The heuristic for solving this type of puzzle is not to check every possibility. Rather, it’s to think of the word as DE _ _ TY, and then check your mental dictionary for words that fit the pattern. It may help to know that the answer isn’t two consonants, but most puzzle solvers would have suspected as much from the outset. In the English language, only SOVEREIGNTY, THIRSTY, and BLOODTHIRSTY end with two consonants followed by TY.
Below are five-letter math words for which the middle letter can be changed to two new letters to form a six-letter word. (Note that the answers aren’t necessarily mathy.)
DIGIT :: DI _ _ IT (unique)
POINT :: PO _ _ NT
FOCUS :: FO _ _ US
MODEL :: MO _ _ EL (unique)
POWER :: PO _ _ ER
RANGE :: RA _ _ GE (unique)
SOLID :: SO _ _ ID (unique)
SPEED :: SP _ _ ED
And below, your challenge is reversed: Find the five-letter word that was changed to form a six-letter math word.
CO _ EX :: CONVEX (unique)
LI _ AR :: LINEAR (unique)
OR _ IN :: ORIGIN
RA _ AN :: RADIAN (unique)
SE _ ES :: SERIES
SP _ RE :: SPHERE