20 math riddles (with answers) to challenge your minds

If you’re a fan of mathematics, solving riddles can be a lot of fun. These types of riddles might not appeal to everyone, but some people truly enjoy them. If you know someone who loves math riddles, feel free to use my list of 20 math riddles — complete with answers!

01. The socks riddle

If you have 30 red socks, 20 white socks, and 10 blue socks, how many will you pick to get at least 1 matching pair without looking?
Answer: 4

02. The Equal Sharing

A group of people collects $529. If each person contributes an amount in dollars equal to the total number of people in the group, how many people are in the group?
Answer: 23 people (23 x 23 = 529)

03. The weight riddle

Three animals—an elephant, a lion, and a monkey—are weighed in pairs on a scale:
The elephant and the 2 crocodiles together weigh 1,200 kg.
The 2 crocodiles and 4 monkeys together weigh 400 kg.
The elephant and 4 monkeys together weigh 1,000 kg.
What is the individual weight of each animal?

Answer: Elephant’s weight: 900 kg, Crocodile’s weight: 150 kg, Monkey’s weight: 25 kg

04. Six to eleven

I add six to eleven and get five. How is this correct?
Hint: What time is it?
Answer: Adding 6 to 11 refers to adding hours on a clock. After 12, the count resets, so 11 + 6 = 5 o’clock.

05. Number sequence

Complete the following sequence: 24, 120, 720, ????
Answer: 5040.
24 is 4! (i.e. 2 x 3 x 4); 120 is 5! (i.e. 2 x 3 x 4 x 5); 720 is 6!, 5040 is 7!.

06. From 0 to 720

How can you make 720 using exactly six zeros and any mathematical operators?
Hint: Use the “!” operator (0! = 1)
Answer: (0!+0!+0!+0!+0!+0!)!=720

07. So many thumbs

Multiply the number of thumbs that everyone in the world has. What is the result?
Answer: 0, because at least one person in the world doesn’t have thumbs.

08. A number that goes away

I am a number, but when you add ‘G’ to me, I go away. What number am I?
Answer: One (gOne).

09. The 2 faced polygon

A polygon is defined as “a closed figure made up of line segments (not curves)”. How can you make a 2 faced polygon?
Answer: Draw it on a sphere like this:

10. Many eights

Using only addition, combine eight 8s to make the number 1,000.
Answer: 8 + 8 + 8 + 88 + 888 = 1000

11. Banana helps against cramps

3 monkeys share a bunch of bananas. The first monkey takes 3 bananas. The second monkey then takes half of the remaining bananas. The third monkey takes the last banana.
How many bananas were in the original bunch?
Answer: 5

12. The Farm Puzzle

On a farm, there are ducks and cows. There are 18 legs and 7 heads in total. How many ducks are there?
Answer: 5 ducks and 2 cows.

13. The Age Gap

A dad is 36 years old, and his son is 6. So in how many years will the father’s age be four times his son’s age?
Answer: In 6 years. (Father will be 42, and the son will be 12, making 42 = 4 × 12)

14. The strangest jetlag in the world

There are Diomedes islands. We’re in winter. It’s 23:00 on the Russian Big Diomede. What time is it on the American Small Diomede island?
Answer: 03:00

15. The School Problem

A school has 120 students. 75 of them play baseball, 60 play soccer, and 30 play both. How many students play neither sport?
Answer: 15 students.

16. The Age Puzzle

A person’s age is five times what it was 12 years ago. So how old is the person now?
Answer: 12 years old.

17. The Sharing Puzzle

Two people have $100 in total. One has $40 more than the other. How much does each have?
Answer: $30 and $70.

18. The Train Puzzle

A train leaves the station at 15:00, traveling at 240 kph. Another train leaves the same station at 16:00, traveling at 360 kph. When will the second train catch up?
Answer: At 18:00. (They’ll meet after 2 hours.)

19. The Walking Puzzle

A person walks 3 km south, then 4 km east. What is the straight-line distance from their starting point?
Answer: 5 km. (Use the Pythagorean theorem)

20. The two pages

Bob opened a book and discovered that the sum of these two-page numbers was 21. But what do you get if you multiply these two numbers?
Answer: 10 x 11 = 110