50 math riddles with answers

Number riddles from quick mental math to tricky puzzles. Work each one out, then open the answer to check the working.

50 riddles · Math riddles with answers · answers included

Updated 13 Oct 2026

Quick mental math

1
If you have a bowl with six apples and you take away four, how many do you have?

easy

Answer
Four.
You took four apples, so those four are the ones you have.
2
I am thinking of a number. Multiply it by 3, subtract 4, and you get 20. What is my number?

easy

Answer
8.
Work backward: 20 + 4 = 24, and 24 ÷ 3 = 8.
3
Double me, then add me once more, and you get 36. What number am I?

easy

Answer
12.
Doubling and adding once more makes three of me: 36 ÷ 3 = 12.
4
If you multiply me by any number, the answer is always me. What number am I?

easy

Answer
Zero.
Any number times 0 is 0.
5
How many legs do 3 dogs, 2 birds and 1 goldfish have altogether?

easy

Answer
16.
Dogs: 3 × 4 = 12. Birds: 2 × 2 = 4. A goldfish has none. 12 + 4 = 16.
6
How many sides do a triangle, a square and a hexagon have altogether?

easy

Answer
13.
3 + 4 + 6 = 13.
7
What comes next: 2, 3, 5, 7, 11, ...?

easy

Answer
13.
These are the prime numbers, which divide evenly only by 1 and themselves.

Think it through

8
Five machines make five toys in five minutes. How long do 100 machines take to make 100 toys?

medium

Answer
5 minutes.
Each machine makes one toy in five minutes, so 100 machines make 100 toys in the same five minutes.
9
I am a three-digit number. My tens digit is 5 more than my ones digit, and my hundreds digit is 8 less than my tens digit. What number am I?

medium

Answer
194.
The hundreds digit is at least 1, so the tens digit is 9 and the hundreds digit is 1. The ones digit is 9 − 5 = 4.
10
I am a two-digit number. My digits add up to 10, and my tens digit is 4 more than my ones digit. What number am I?

medium

Answer
73.
Two digits 4 apart that add to 10 are 7 and 3, with the larger one in the tens place.
11
What is the smallest positive whole number that 1, 2, 3, 4, 5 and 6 all divide into evenly?

medium

Answer
60.
It needs the factors 4, 3 and 5: 4 × 3 × 5 = 60, and 60 is also divisible by 2 and 6.
12
A number multiplied by itself, plus the number, equals 42. What is the number, if it is positive?

medium

Answer
6.
6 × 6 = 36, and 36 + 6 = 42.
13
An hour and a half ago it was 2:45. What time will it be 40 minutes from now?

medium

Answer
4:55.
Now it is 2:45 + 1:30 = 4:15, and 40 minutes later it is 4:55.
14
A book's pages are numbered 1 to 50. How many digits are printed in the page numbers?

medium

Answer
91.
Pages 1 to 9 use 9 digits. Pages 10 to 50 are 41 pages with 2 digits each, which is 82. 9 + 82 = 91.
15
A train leaves at 10:40 in the morning and arrives at 1:15 in the afternoon. How long is the trip?

medium

Answer
2 hours 35 minutes.
10:40 to 12:40 is 2 hours, and 12:40 to 1:15 is 35 minutes.

Tricky puzzles

16
A clock strikes six times in 5 seconds, with equal gaps between the strikes. How long does it take to strike twelve times?

hard

Answer
11 seconds.
Six strikes have five gaps, so each gap lasts 1 second. Twelve strikes have eleven gaps.
17
If you write every whole number from 1 to 100, how many times do you write the digit 9?

hard

Answer
20 times.
Ten numbers end in 9 (9, 19 and so on up to 99) and ten numbers from 90 to 99 start with 9. 99 is counted in both groups because it has two 9s.
18
Half of a number is 4 more than a third of it. What is the number?

hard

Answer
24.
Half of 24 is 12 and a third of 24 is 8, and 12 is 4 more than 8.
19
What is 1 + 2 + 3 and so on all the way to 20?

hard

Answer
210.
Pair the ends: 1 + 20, 2 + 19 and so on make 10 pairs of 21, and 10 × 21 = 210.

Patterns, timers and schedules

20
Double a number, then add 6, and the result is 20. Which number did you start with?

easy

Answer
7, because 2 x 7 + 6 = 20.
Subtracting 6 from 20 gives 14, and halving 14 gives 7.
21
Three positive whole numbers have the same sum and product. What are they?

medium

Answer
1, 2, and 3. Both the sum and product are 6.
Adding 1 + 2 + 3 and multiplying 1 x 2 x 3 both produce 6.
22
Using exactly three 3s, addition, and multiplication, make 12.

easy

Answer
3 x 3 + 3 = 12.
Multiplication is evaluated first, giving 9, and adding the final 3 gives 12.
23
Twelve eggs cost $6 at a constant per-egg price. What do three eggs cost?

easy

Answer
$1.50.
Each egg costs $0.50, so three eggs cost 3 x $0.50 = $1.50.
24
Find the smallest positive whole number equal to seven times the sum of its digits.

hard

Answer
21, because 2 + 1 = 3 and 7 x 3 = 21.
Testing positive multiples of 7 in order, 21 is the first whose digit sum, 3, becomes the number when multiplied by 7.
25
A number is halved, then 8 is added, giving 15. What was the number?

easy

Answer
14.
Subtracting 8 from 15 leaves 7, and doubling 7 reverses the halving.
26
A rectangle has perimeter 30 units and length 9 units. What is its width?

medium

Answer
6 units.
The length and width sum to half the perimeter, 15. Subtracting length 9 leaves width 6.
27
Five equal boxes contain 35 marbles altogether. How many marbles are in each box?

easy

Answer
7 marbles.
Dividing 35 marbles equally among 5 boxes gives 35 / 5 = 7.
28
Continue the description sequence: 1, 11, 21, 1211, 111221. What comes next?

hard

Answer
312211, because 111221 contains three 1s, two 2s, and one 1.
Reading 111221 in groups gives three 1s, two 2s, and one 1, encoded as 31 22 11.
29
Spot the growing gaps: 2, 3, 5, 8, 12, 17. Which number follows?

medium

Answer
23. The gaps are 1, 2, 3, 4, 5, then 6.
The amount added increases by 1 each time, so adding 6 to 17 gives 23.
30
Squares are hiding here: 1, 4, 9, 16. Name the next term.

easy

Answer
25, which is 5 squared.
The terms are consecutive squares from 1 squared through 4 squared, so the next is 5 squared.
31
Products of neighbors form 2, 6, 12, 20, 30. What is the next product?

medium

Answer
42, from 6 x 7.
The terms are 1 x 2, 2 x 3, 3 x 4, 4 x 5, and 5 x 6, so 6 x 7 follows.
32
Divide by the same number each time: 81, 27, 9, 3. What comes next?

easy

Answer
1. Each term is the previous term divided by 3.
Every term is one third of the previous term, so 3 divided by 3 is 1.
33
Following 3, 5, 8, 13, each term combines the previous two. Which number is next?

easy

Answer
21.
Adding the previous two terms, 8 + 13, gives 21.
34
Growing by multiples of three, the sequence reads 4, 7, 13, 22, 34. What follows?

medium

Answer
49.
The gaps are 3, 6, 9, and 12. The next gap is 15, so 34 + 15 = 49.
35
A bell rings on beat 1 and then every fourth beat. On which beat does it ring for the fourth time?

medium

Answer
Beat 13.
The ring beats are 1, 5, 9, and 13.
36
Two repeating timers start together. One ends every 6 minutes and the other every 8 minutes. After how many minutes do they next end together?

medium

Answer
24 minutes.
Twenty-four is the first positive time divisible by both 6 and 8.
37
The rehearsal begins at 2:10 and lasts 35 minutes. At what time does it end?

easy

Answer
2:45.
Adding 35 minutes to 2:10 gives 2:45.
38
A shuttle leaves at 9:02 and then every 7 minutes. What is its first departure after 9:20?

medium

Answer
9:23.
The departures are 9:02, 9:09, 9:16, and 9:23.
39
A light alternates on and off once per beat. It is on at beat 1. What is its state at beat 12?

easy

Answer
Off.
Odd-numbered beats are on and even-numbered beats are off.
40
A countdown begins at 18 and drops by 3 each step. What does it show after four drops?

easy

Answer
6.
The four drops produce 15, 12, 9, and 6.
41
An alarm rings at 4:12 and then every 5 minutes. Counting the ring at 4:12, how many times has it rung by 4:32?

medium

Answer
Five times.
It rings at 4:12, 4:17, 4:22, 4:27, and 4:32.
42
A machine repeats three phases in order: hum, click, rest. Its first phase is hum. What phase is number 14?

medium

Answer
Click.
Every third phase is rest. Phase 13 returns to hum, so phase 14 is click.
43
The first act lasts 12 minutes, the pause lasts 3, and the second act lasts 15. If everything starts at 7:30, when does it finish?

medium

Answer
8:00.
The full duration is 30 minutes, taking 7:30 to 8:00.
44
Three signals begin together. They repeat every 4, 6, and 9 minutes. After how many minutes do all three next occur together?

hard

Answer
36 minutes.
Thirty-six is the smallest positive multiple shared by 4, 6, and 9.
45
A one-minute task is done three times with a two-minute pause after each of the first two attempts. How long does the full sequence take?

medium

Answer
7 minutes.
Three minutes of work plus two pauses of two minutes totals seven minutes.
46
A display advances through A, B, C, D, then repeats. It shows C now. What will it show after seven advances?

medium

Answer
B.
Seven advances equal one full cycle plus three more: D, A, B.
47
A meeting starts 20 minutes before noon and lasts 45 minutes. When does it end?

medium

Answer
12:25.
Twenty minutes brings the meeting to noon, leaving 25 minutes after noon.
48
Five speakers each use 4 minutes, with a 1-minute changeover between speakers. How long from the first start to the final finish?

hard

Answer
24 minutes.
The talks use 20 minutes and the four changeovers use 4 more.
49
A door unlocks for every third chime, beginning with chime 3. It has just unlocked at chime 18. At which chime will it next unlock?

easy

Answer
Chime 21.
Unlocking chimes are consecutive multiples of three.
50
A timer shows 10 for one second, then 9 for one second, continuing through 0. How long does it display a number?

hard

Answer
11 seconds.
It displays eleven values, from 10 through 0 inclusive, for one second each.

Timer and team scores

Seconds per turnTurns in the session

8 turns × 60 seconds = 8 minutes of play, plus instructions and breaks.

Pause whenever the group needs more time.

Teams

Team Lime's turn

Team Lime: 0

Team Violet: 0

Use this set with a group

Read a prompt, allow thinking time, then invite an answer or a pass. For a timed round, choose a turn length before starting. A host can keep the printed answers out of view until the round ends.

Games and printables

Find a game