Math Riddles with Answers
You don't need to love math to enjoy these. Most math riddles here need logic more than arithmetic. Grab some paper if you want, then check your work against the answer.
Easy math riddles for kids
Several need nothing beyond counting and a careful read. The fishing trip with two fathers and two sons is a classic starter.
Math riddles with answers for adults
The hen and a half problem still trips up engineers. Answers walk through the working, not just the number.
Number puzzles with hints
35 of these 48 riddles include a hint, so a wrong turn never has to end the run.
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1. Two fathers and two sons went fishing. Each caught one fish, yet they brought home only three fish. How is that possible?
Need a hint?
Count the people, not the roles.
Show answer
There were only three people. A grandfather, his son, and his grandson make two fathers and two sons.
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2. I am a number. Multiply me by any other number and the answer never changes. What am I?
Need a hint?
I am worth nothing on my own.
Show answer
Zero. Any number times zero is always zero.
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3. I am thinking of a number. Triple it and add 12, and you get the same total as multiplying it by 5 and subtracting 4. What is my number?
Need a hint?
The two totals match, so the extra 16 must equal two more copies of the number.
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8. Both recipes give 36, since 3 times 8 plus 12 equals 5 times 8 minus 4.
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4. A brick weighs one kilogram plus half a brick. How much does the whole brick weigh?
Need a hint?
Put half a brick on each side of the scale.
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Two kilograms. If half a brick weighs one kilogram, the whole brick weighs two.
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5. A bat and a ball cost 1 dollar and 10 cents together. The bat costs exactly one dollar more than the ball. How much is the ball?
Need a hint?
The obvious answer of 10 cents makes the difference only 90 cents.
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5 cents. Then the bat costs 1.05, which is exactly one dollar more.
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6. A patch of lily pads doubles in size every day and covers the whole lake in 48 days. On which day did it cover half the lake?
Need a hint?
Work backwards from the last day.
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Day 47. One more doubling turns half a lake into a full lake.
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7. If 5 machines take 5 minutes to make 5 widgets, how long would 100 machines take to make 100 widgets?
Need a hint?
Figure out how long one machine needs for one widget.
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5 minutes. Each machine makes one widget in 5 minutes, no matter how many machines run at once.
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8. A tailor has a 30 meter roll of cloth and cuts off a 3 meter piece every day. On which day does she make her last cut?
Need a hint?
The last piece never needs a cut of its own.
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Day 9. The ninth cut splits the final 6 meters into two pieces, so there is nothing left to cut on day 10.
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9. Which three whole numbers give the same result whether you add them or multiply them?
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1, 2 and 3. Both the sum and the product equal 6.
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10. Divide 30 by half and add 10. What do you get?
Need a hint?
Dividing by a half is not the same as dividing in half.
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70. Dividing by a half doubles a number, so 30 becomes 60, plus 10 is 70.
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11. A farmer has 17 sheep. All but 9 run away. How many sheep are left?
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9. The phrase all but 9 means exactly 9 stayed behind.
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12. What comes next in this sequence: 1, 11, 21, 1211, 111221?
Need a hint?
Say the previous number out loud, digit by digit.
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312211. Each term reads the previous one out loud, so three 1s, two 2s, one 1.
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13. Count upward from one. Which number is the first whose English name contains the letter a?
Need a hint?
You will be counting for quite a while.
Show answer
One thousand. Every number from 1 to 999 avoids the letter a completely.
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14. Which is bigger, six dozen dozen or half a dozen dozen?
Need a hint?
Turn each phrase into a multiplication before comparing.
Show answer
Six dozen dozen. That works out to 864, while half a dozen dozen is only 72.
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15. Maya's purse holds twice as many dimes as quarters, and the coins add up to 90 cents. How many quarters does she have?
Need a hint?
Group every quarter with its two dimes and price the bundle.
Show answer
Two. Each quarter travels with two dimes, and two of those 45 cent bundles make 90 cents.
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16. A snail climbs 3 meters up a 10 meter well each day and slips back 2 meters each night. How many days does it take to get out?
Need a hint?
The last day is different from all the others.
Show answer
8 days. It gains 1 meter per full day, and on day 8 it climbs from 7 meters to the top before the night slip.
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17. There are 4 apples in a basket and you take away 3. How many apples do you have?
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3. You took them, so those are the ones you have.
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18. How can half of nine be four?
Need a hint?
Think in Roman numerals.
Show answer
Write nine as the Roman numeral IX and cut it in half horizontally. The top half reads IV, which is four.
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19. What comes next in this sequence: 2, 3, 5, 9, 17?
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33. Each number is double the previous one minus 1.
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20. A father is four times as old as his son. In 20 years he will only be twice as old. How old is the son now?
Need a hint?
Try setting the son's age to a small round number.
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10. The father is 40, and in 20 years they will be 60 and 30, which fits both facts.
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21. Three friends pay 30 dollars for a room. The clerk refunds 5, the bellboy keeps 2 and hands each friend 1 back. The friends paid 27 and the bellboy has 2, which makes 29. Where did the missing dollar go?
Need a hint?
You should subtract the 2, not add it.
Show answer
There is no missing dollar. The 27 they paid already includes the bellboy's 2, so adding it again counts it twice.
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22. In a strange pet shop a duck costs 9 dollars, a spider costs 36 dollars and a bee costs 27 dollars. How much does a cat cost?
Need a hint?
Count the legs of each animal.
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18 dollars. The shop charges 4.50 per leg, and a cat has four legs.
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23. What is the smallest number that grows by 12 when you turn it upside down?
Need a hint?
Only some digits still look like digits upside down.
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86. Turned upside down it reads 98, which is exactly 12 more.
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24. How many eggs can you put into an empty basket one meter wide?
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Only one. After the first egg the basket is no longer empty.
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25. A hen and a half lays an egg and a half in a day and a half. How many eggs do 9 hens lay in 9 days?
Need a hint?
First work out what a single hen does in a single day.
Show answer
54. One hen lays two thirds of an egg per day, so 9 hens times 9 days times two thirds gives 54.
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26. Two ducks walk in front of a duck, two ducks walk behind a duck, and one duck walks in the middle. What is the smallest number of ducks?
Need a hint?
The same ducks can play more than one role.
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3. Three ducks in a single row satisfy all three descriptions at the same time.
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27. Which number has exactly as many letters in its name as its own value?
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Four. The word four is spelled with exactly four letters.
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28. When does 11 plus 2 equal 1?
Need a hint?
Stop thinking in plain arithmetic and look at the wall.
Show answer
On a clock. Two hours after 11 o'clock it is 1 o'clock.
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29. What comes next in this sequence: 1, 4, 9, 16, 25?
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36. These are the square numbers, and 6 times 6 is 36.
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30. Using eight 8s and nothing but addition, how do you make exactly 1000?
Need a hint?
Start with the biggest chunk you can build from 8s.
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888 + 88 + 8 + 8 + 8. Those five numbers use eight 8s and add up to exactly 1000.
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31. A 100 kg watermelon is 99 percent water. After a day in the sun it is only 98 percent water. What does it weigh now?
Need a hint?
Track the part that does not evaporate.
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50 kg. The 1 kg of dry matter must now make up 2 percent of the whole, so the whole is 50 kg.
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32. If 3 cats catch 3 mice in 3 minutes, how many cats are needed to catch 100 mice in 100 minutes?
Need a hint?
Work out the catch rate of a single cat.
Show answer
Still 3. Each cat catches one mouse every 3 minutes, so 3 cats catch about 100 mice in 100 minutes.
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33. What was the most recent year in the past that reads the same when turned upside down?
Need a hint?
Only 0, 1, 6, 8 and 9 survive the flip.
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1961. Flip the digits and they still read 1961.
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34. What is half of a half of a half of 8?
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1. Halving 8 three times gives 4, then 2, then 1.
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35. I am a two digit number. My digits add up to 9, and if you reverse my digits I grow by exactly 27. What am I?
Need a hint?
The difference of 27 tells you the digits are 3 apart.
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36. Reversed it becomes 63, which is 27 more, and 3 plus 6 equals 9.
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36. A rooster sits on the exact peak of a barn roof and lays an egg. Which side of the roof does the egg roll down?
Need a hint?
Check who is doing the laying.
Show answer
Neither side. Roosters do not lay eggs.
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37. Add up every whole number from 1 through 100. What total do you get?
Need a hint?
Pair the smallest number with the largest and watch the pattern.
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5050. Pair 1 with 100, 2 with 99, and so on: fifty pairs that each add up to 101.
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38. You have exactly 100 dollars and must buy exactly 100 animals. Cows cost 10 dollars, pigs cost 3 dollars and chickens cost 50 cents. What do you buy?
Need a hint?
You will need a lot of chickens.
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5 cows, 1 pig and 94 chickens. That is exactly 100 animals for exactly 100 dollars.
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39. What comes next in this sequence: 3, 6, 12, 24?
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48. Each number is double the one before it.
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40. Multiply me by 4, then subtract 6, and you get three times me. What number am I?
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6. Four times 6 is 24, minus 6 is 18, and 18 is three times 6.
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41. Take 1000 and add 40. Add another 1000. Add 30. Add 1000 again. Add 20. Add 1000 one more time. Add 10. What is the total?
Need a hint?
Add the thousands and the small numbers separately.
Show answer
4100. Most people blurt out 5000 because the small additions feel like they build another thousand.
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42. Which two whole numbers multiply together to make exactly 31?
Show answer
1 and 31. It is a prime number, so no other pair of whole numbers works.
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43. How much dirt is in a hole that is 2 meters long, 2 meters wide and 2 meters deep?
Show answer
None. A hole is empty, that is what makes it a hole.
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44. I doubled my money, spent 10 dollars, doubled what was left, spent 10 more and ended up with exactly 10 dollars. How much did I start with?
Need a hint?
Undo each step in reverse order.
Show answer
10 dollars. Work backwards: 10 plus 10 is 20, halve it to 10, add 10 to get 20, halve it to 10.
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45. A knockout tournament starts with 64 players, and one loss sends you home. How many matches decide the champion?
Need a hint?
Count the losers instead of the rounds.
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63. Every match eliminates exactly one player, and 63 players must go home before a champion remains.
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46. What is unusual about the number 8549176320?
Need a hint?
Spell each digit out as a word.
Show answer
Its digits appear in alphabetical order: eight, five, four, nine, one, seven, six, three, two, zero.
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47. In two years I will be twice as old as I was five years ago. How old am I now?
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12. In two years I will be 14, which is double the 7 I was five years ago.
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48. Multiply together every number on a telephone keypad. What do you get?
Need a hint?
Do not forget the bottom row.
Show answer
Zero. The keypad includes a 0, and anything multiplied by zero is zero.
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FAQ about Math Riddles with Answers
Do I need to be good at math to solve these?
No. Most math riddles here reward careful reading over calculation. If you can add and multiply small numbers, the rest is logic.
Do the answers explain the working?
Yes. Answers show the reasoning, like why nine hens over nine days give 54 eggs, so you learn the method rather than just the result.
Are these math riddles good for school?
Teachers use them as warmups and early finisher tasks. They fit upper elementary through high school, and the hints let students help themselves when they get stuck.
If the logic side pulled you in more than the numbers, try our Logic Riddles with Answers. For a wider mix of quick stumpers, browse the Brain Teasers with Answers.