Mental Math
Vocabulary
Fun Facts
Riddles
Other
100

What is 23 × 4 + 19?

111

100

What’s the term for the distance around a circle?

Circumference

100

What is the sum of the digits in any 2-digit multiple of 9?

9

100

What two whole numbers multiply to 36 and add up to 13?

9 and 4

100

What is the smallest positive integer that is divisible by 3, 4, 5, and 6?

60
200

A number is increased by 15%, and the result is 253. What was it?

220
200

What do we call a number that can be expressed as a fraction of integers?

Rational number

200

What number has the same number of letters as its value?

Four

200

I am a 2-digit number. Reversed and added to myself, I equal 121.

77

200

Solve for x: 2(x + 3) = 4x - 6.

6

300

What is 375 ÷ 25 × 1.6?

24

300

What’s the term for the smallest positive number divisible by given numbers?

Least Common Multiple (LCM)

300

What number do you always get from the 1089 number trick?

1089
300

I am less than 20 and a multiple of both 2 and 3. What number am I?

6,12,18

300

111,111,111 x 111,111,111 = 

12,345,678,987,654,321

400

Subtract 387 from 1000, then multiply the result by 0.25.

153.25

400

What is a rational function?

A ratio of two polynomials

400

What is the name of the sequence where each number is the sum of the two before it?

Fibonacci sequence

400

I have two U.S. coins that add up to 30 cents.
One of them is not a nickel.
What are the two coins?

a nickel and a quarter

400

What temperature is the same in both Celsius and Farenheit?

-40 degrees

500

What is 51² – 49²?

200
500

What does it mean if a set is countably infinite?

Its elements can be listed in a sequence (1-to-1 with natural numbers)

500

What math object has infinite length but encloses finite area?

Gabriel’s Horn (or Torricelli’s trumpet)

500

If a student and a half write a paper and a half in a day and a half, how many papers will half a dozen students write in a dozen days?

48

500

Complete the sequence:

1, 11, 21, 1211, 111221,

312211