12 Math Knock-Knock Jokes

In a very old Second City skit, a man on hold complained (to no one in particular) about the hold music. After his complaint, a voice on the other end of the line said, “I’m sorry. Don’t you like my singing?”

“Who are you?” he asked, surprised.

“I’m your hold operator. If you don’t like music, I’d be happy to entertain you in some other way. Would you like to hear a joke?” she asked.

“Um… sure, why not?”

“It’s a knock-knock joke,” she said. “Are you familiar with the format?”

Now, that’s just funny!

My favorite joke to tell in the classroom is a knock‑knock joke, so I hope that you are familiar with the format.

Knock, knock.
Who’s there?
Interrupting cow.
Interrup — ?
Moo!

My sons are now of an age where they can understand jokes, and those of the knock‑knock variety are told daily in our house. (The knock-knock jokes at GRiN are a source of endless amusement.) Sadly, I didn’t know any knock‑knock jokes that are mathy… so I made some up. Here they are, 12 totally original (sort of) but not terribly funny math knock-knock jokes. Aren’t you glad you stopped by today?

Knock, knock.
Who’s there?
Lemma.
Lemma who?
Lemma in, it’s raining!

Knock, knock.
Who’s there?
Mode.
Mode who?
Mode the lawn. What should I do next?

Knock, knock.
Who’s there?
Slope.
Slope who?
Slope ups should stay on the porch.

Knock, knock.
Who’s there?
Convex.
Convex who?
Convex go to prison!

Knock, knock.
Who’s there?
Prism.
Prism who?
Prism is where convex go!
(Weren’t you paying attention to the previous joke?)

Knock, knock.
Who’s there?
Origin.
Origin who?
Vodka martini origin fizz?

Knock, knock.
Who’s there?
Zeroes.
Zeroes who?
Zeroes as fast as she can, but the boat doesn’t move.

Knock, knock.
Who’s there?
Unit.
Unit who?
Unit socks; I knit sweaters.

Knock, knock.
Who’s there?
Outlier.
Outlier who?
Outlier! We only let honest people in this house!

Knock, knock.
Who’s there?
Möbius.
Möbius who?
Möbius a big whale!

Knock, knock.
Who’s there?
Tangents.
Tangents who?
Tangents spend a lot of time at the beach.

Knock, knock.
Who’s there?
Axis.
Axis who?
Axis for chopping, saw is for cutting.

Ordered Pairs, Gumby, and Palindromes

My sons recently received green, flexible toys from their aunt. When I turned on my calculator today, it read:

(2, GUMBYS)

I’m not sure why it’s an ordered pair, but seeing that on my calculator screen cracked me up.

Then tonight at dinner, they made up their own knock-knock joke:

Knock, knock.
Who’s there?
Gumby.
Gumby who?
Gumby more fun to chew than anything else!

While I’m happy that my four-year-old sons have a sense of humor, it’s their love of math that I most appreciate. Yesterday in the car, Eli noted that the time was 6:16 p.m. “Palindrome!” he shouted.

“Actually,” Alex said, “any time that it’s six, colon, number, six, it’s a palindrome.”

“That’s right,” I said. “How many times a day do you think the time is a palindrome?”

Eli guessed 50. Alex guessed 70. But those were clearly random guesses. I asked if they could figure it out.

“We could count them,” Eli suggested.

“No,” Alex said. “An easier way is, ‘What is 24 × 6?'”

“Why would 24 × 6 give you the answer?” I asked, mainly because I was sure he didn’t know.

“Because there are 24 hours in a day,” he said, “and there are 6 times each hour — when the middle number is 0, 1, 2, 3, 4, or 5.” He then used the distributive property to calculate 24 × 6 = (20 + 4) × 6 = 120 + 24 = 144.

“No,” Eli said. “There aren’t 6 palindromes at 10 o’clock.”

They discussed it for a while, and they agreed that there was only one palindrome of the form 10:_1, 11:_1, and 12:_1. And using that piece of info, they jointly concluded that there are 18 hours in a day with 6 palindromes and 6 hours in a day with just 1 palindrome, giving a total of 114 palindromes per day.

Though none of them are as good as these:

One? No!
Six axis.
Seven eves.
Nine men in. (A palindrome about nine, with nine letters, and an allusion to baseball, which has nine players per team. Sweet!)
Tenet.

Some people love the smell of napalm in the morning, but I love listening to two kids solve a math problem. I may even love it more than I love a good Gumby joke!