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20 Math Riddles With Answers
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1. What is half of two plus two?
Three (half of two is one, plus two).
2. If two's company and three's a crowd, what are four and five?
Nine.
3. 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?
194.
4. How can you add eight 8s to get 1,000?
888 + 88 + 8 + 8 + 8 = 1,000.
5. A bat and a ball cost $1.10. The bat costs $1.00 more than the ball. How much is the ball?
5 cents.
6. When I was 6, my sister was half my age. Now I'm 70. How old is my sister?
67.
7. What three positive numbers give the same answer whether you add them or multiply them?
1, 2 and 3.
8. If 5 machines take 5 minutes to make 5 widgets, how long would 100 machines take to make 100 widgets?
5 minutes.
9. A lily pad patch doubles in size every day and covers a lake in 48 days. How long to cover half the lake?
47 days.
10. Divide 30 by half and add 10. What do you get?
70 (30 ÷ ½ = 60, plus 10).
11. Which weighs more: 1 kg of iron or 1,000 g of cotton?
They weigh the same.
12. What number do you get when you multiply all the numbers on a phone keypad?
Zero (because of the 0).
13. How many times can you subtract 10 from 100?
Once; after that you're subtracting from 90.
14. A clock strikes 6 times in 5 seconds. How long does it take to strike 12 times?
11 seconds (5 gaps take 5 seconds, so 11 gaps take 11).
15. What is the smallest whole number that is spelled with the letter A?
One thousand.
16. If you count from 1 to 100, how many 7s will you pass?
20.
17. What is 1 + 1 × 0?
1 (multiply first: 1 × 0 = 0, then 1 + 0).
18. A brick weighs 1 kg plus half a brick. How much does a whole brick weigh?
2 kg.
19. If a dozen eggs cost $3, how much does one egg cost?
25 cents.
20. How many sides does a circle have?
Two: inside and outside (a riddle answer).