Math Riddles With Answers
Updated · Best Riddles With Answers editorial team
Quick answer: This page offers 42 math riddles with answers, covering sums, fractions, shapes, speed and number logic. It suits students, parents and anyone who enjoys a mental workout. Every answer shows the working in one short clause, so you can check the method as well as the result. Start with the easy set and build up to the hard riddles.
Easy Math Riddles
You have 5 apples, eat 2, then buy 4 more. How many apples do you have?
7, because 5 - 2 = 3 and 3 + 4 = 7.
How many sides do a triangle and a square have all together?
7, because 3 + 4 = 7.
A carton holds 12 eggs. You use a quarter of them. How many are left?
9, because a quarter of 12 is 3 and 12 - 3 = 9.
Double a number and add 3 and you get 11. What is the number?
4, because 4 x 2 = 8 and 8 + 3 = 11.
A spider has 8 legs. How many legs do 3 spiders have?
24, because 3 x 8 = 24.
A film lasts 2 hours and 15 minutes. How many minutes is that?
135, because 2 x 60 = 120 and 120 + 15 = 135.
What is 9 + 9 - 9 + 9 - 9?
9, because 9 + 9 = 18, 18 - 9 = 9, 9 + 9 = 18 and 18 - 9 = 9.
A farmer has 10 sheep. All but 3 run away. How many are left?
3. All but 3 means 3 stayed.
How many 20 cent coins make 2 dollars?
10, because 2 dollars is 200 cents and 200 / 20 = 10.
Half of a number is 15. What is the number?
30, because 15 x 2 = 30.
There are 7 days in a week. How many days are there in 4 weeks?
28, because 4 x 7 = 28.
Tom has 6 stickers and Sara has twice as many. How many do they have together?
18. Sara has 12 and 6 + 12 = 18.
Trickier Math Riddles
A drawer holds loose red and blue socks and the light is off. What is the smallest number of socks you must pull out to be sure of a matching pair?
3. With only two colours, the third sock must match one of the first two.
What is 100 divided by a half, minus 50?
150, because 100 / 0.5 = 200 and 200 - 50 = 150.
A doctor gives you 3 pills and tells you to take one every half hour. How long do they last?
1 hour. You take pills at 0, 30 and 60 minutes.
Divide 30 by a half and add 10. What do you get?
70, because 30 / 0.5 = 60 and 60 + 10 = 70.
12 people are on a bus. At the first stop 5 get off and 3 get on. At the second stop 4 get off and 6 get on. How many are on the bus now?
12. First stop: 12 - 5 + 3 = 10. Second stop: 10 - 4 + 6 = 12.
A garden is 8 metres long and 5 metres wide. How much fencing goes all the way round it?
26 metres, because 8 + 5 + 8 + 5 = 26.
How many times can you subtract 5 from 25?
Once. After that you are subtracting from 20, not 25.
I think of a number, add 7 and multiply by 3 to get 36. What was my number?
5. Working back: 36 / 3 = 12 and 12 - 7 = 5.
A train travels at 60 kilometres an hour for two and a half hours. How far does it go?
150 kilometres, because 60 x 2.5 = 150.
A pizza has 8 slices. Three friends eat 2 slices each. What fraction of the pizza is left?
A quarter. They eat 3 x 2 = 6 slices, leaving 2, and 2 / 8 = 1/4.
Which three whole numbers give the same result whether you add them or multiply them?
1, 2 and 3, because 1 + 2 + 3 = 6 and 1 x 2 x 3 = 6.
A dozen eggs cost 3.60 dollars. How much does one egg cost?
30 cents, because 360 cents / 12 = 30 cents.
Hard Math Riddles
Three consecutive whole numbers add up to 72. What are they?
23, 24 and 25. The middle number is 72 / 3 = 24, and 23 + 24 + 25 = 72.
If 5 machines take 5 minutes to make 5 widgets, how long do 100 machines take to make 100 widgets?
5 minutes. Each machine makes one widget in 5 minutes, so 100 machines make 100.
What is the sum of all the whole numbers from 1 to 100?
5050. There are 50 pairs (1 + 100, 2 + 99 and so on) and each pair makes 101, so 50 x 101 = 5050.
A rectangle is three times as long as it is wide, and its perimeter is 48 centimetres. What is its area?
108 square centimetres. Width 6, length 18: perimeter 2 x (6 + 18) = 48 and area 6 x 18 = 108.
A tap fills a tank in 6 hours and a drain empties a full tank in 12 hours. With both open, how long does an empty tank take to fill?
12 hours. Each hour the tank gains 1/6 - 1/12 = 1/12 of its volume.
Two trains 300 kilometres apart head toward each other at 70 and 80 kilometres an hour. When do they meet?
After 2 hours. They close the gap at 70 + 80 = 150 km/h, and 300 / 150 = 2.
A coat costs 80 dollars after a 20 percent discount. What was the original price?
100 dollars. 80 is 80 percent of the price, so 80 / 0.8 = 100.
Two numbers add up to 20 and differ by 6. What are they?
13 and 7, because 13 + 7 = 20 and 13 - 7 = 6.
Six people each shake hands once with every other person. How many handshakes are there?
15. Each of 6 people shakes 5 hands, and 6 x 5 = 30, which counts each shake twice: 30 / 2 = 15.
What is the smallest number that all of 1, 2, 3, 4, 5 and 6 divide into exactly?
60, because 60 / 4 = 15, 60 / 5 = 12, 60 / 6 = 10, and 60 is also divisible by 2 and 3.
Quick-Fire Math Riddles
A shape with six equal sides, used by bees.
Hexagon.
A round shape with no corners and no straight sides.
Circle.
Any number times me gives me.
Zero.
Half of a half.
A quarter.
A shape with three sides and three corners.
Triangle.
A number that only divides by 1 and itself.
Prime number.
Four equal sides and four right angles.
Square.
The number of eggs in a standard box.
A dozen (12).
How to Use These Riddles
Math riddles work best when you slow down. Read the question twice, write the numbers down, and work through it one step at a time before looking at the answer. Many wrong answers come from rushing at the first number you see.
Teachers can use the easy set as a warm-up and the hard set for discussion. Ask pupils to explain their method, because a different route to the same answer is a sign of real understanding.
Frequently Asked Questions
What is the answer to the sheep riddle: all but 3 run away?
3 sheep are left. The phrase all but 3 means every sheep except 3 ran off, so those 3 stayed. This kind of wording is a common trick in math riddles.
How do you add the numbers from 1 to 100 quickly?
Pair the numbers from each end: 1 + 100, 2 + 99, 3 + 98 and so on. Each pair makes 101 and there are 50 pairs, so the total is 50 x 101 = 5050.
Why do the answers show working?
Showing the working lets you check the method and learn the trick rather than just see a number. If your answer differs, compare your steps with the working to find where they split.
Are these math riddles suitable for children?
Yes. The easy section uses small numbers and familiar objects like apples and stickers, and the later sections add fractions, speed and algebra-style thinking for older children and adults.
