Number riddles and math puzzles for kids, with hints and a short explanation of every answer.
Each number after the first two is the sum of the two before it: 1, 1, 2, 3, 5, 8. What comes next?
Check the rule on the start of the list: 1 + 1 = 2, and 1 + 2 = 3.
Use the last two numbers in the list.
13.
Each new number is the two before it added together: 1 + 1 = 2, 1 + 2 = 3, 2 + 3 = 5, 3 + 5 = 8, and 5 + 8 = 13. This is called the Fibonacci sequence. Its numbers often show up in nature, like the spirals of seeds in a sunflower.
Each number after the first two is the sum of the two before it: 1, 1, 2, 3, 5, 8. What comes next?
Check the rule on the start of the list: 1 + 1 = 2, and 1 + 2 = 3.
Use the last two numbers in the list.
13.
Each new number is the two before it added together: 1 + 1 = 2, 1 + 2 = 3, 2 + 3 = 5, 3 + 5 = 8, and 5 + 8 = 13. This is called the Fibonacci sequence. Its numbers often show up in nature, like the spirals of seeds in a sunflower.
Today is Monday. What day will it be three days from today?
Good to know: "Three days from today" means you start counting with tomorrow.
Count forward one day at a time, starting with tomorrow.
Tomorrow is Tuesday. Keep counting two more days.
Thursday.
Count three days forward from Monday: Tuesday is one, Wednesday is two, and Thursday is three.
I am a whole number greater than 20 and less than 30. I divide exactly by both 3 and 4. What am I?
A number that divides exactly by 3 and by 4 also divides exactly by 12.
Count by 12s: 12, then the next one.
24.
Numbers that divide exactly by both 3 and 4 are the multiples of 12: 12, 24, 36 and so on. The only one between 20 and 30 is 24.
I am a solid shape with exactly six faces, all squares. What am I?
Many building blocks and game dice have this shape.
Ice in a cold drink often comes in this shape.
A cube.
A cube has six flat faces, and every face is a square of the same size. A cube also has 12 edges and 8 corners. A box whose faces are not all squares is called a rectangular prism.
With one straight cut, snip a small triangle off one corner of a square. The cut crosses the two sides that meet at that corner. How many corners does the bigger piece have now?
Good to know: The cut crosses each of the two sides partway along, not through another corner, and only the bigger piece's corners are counted.
Draw a square on paper and try it with one pencil line.
Count the corner the cut takes away, then the new corners it makes where it crosses each side.
Five.
A square has 4 corners. The cut takes away 1 corner, leaving 3. But it makes 2 new corners, one where it crosses each side. 3 + 2 = 5, so the bigger piece is a pentagon, a shape with five corners.
A snail climbs 3 meters each day and slips 2 meters each night. Starting at the bottom, on which day does it first reach the top of a 10-meter wall?
Good to know: The snail starts at the bottom in the morning, climbs 3 meters every day and slips 2 meters every night. Once it reaches the top, it stops and does not slip.
Each day and night together, the snail ends up only 1 meter higher. But watch the very last day.
On its last day, the snail can reach the top before night comes, so it never slips back.
Day eight. It reaches the top that day, so it never slips back down.
After each day and night, the snail is 1 meter higher: at 1 meter after the first night, 2 meters after the second, and 7 meters after the seventh. On day 8 it climbs 3 meters, from 7 to 10, and reaches the top before night. The quick answer, day 10, forgets that last big climb.
A bat and a ball cost $1.10 altogether. The bat costs $1 more than the ball. What does the ball cost?
Good to know: The bat and the ball are the only two things, and the prices are in whole cents.
Test your first guess: add the ball's price and the bat's price. Is the total $1.10, and is the bat exactly $1 more?
If the ball were 10 cents, the bat would be $1.10, and together they would be $1.20. Try a smaller amount.
Five cents. The bat costs $1.05.
If the ball costs 5 cents, the bat costs $1 more: $1.05. Together, $1.05 + $0.05 = $1.10. The quick answer, 10 cents, does not work: the bat would cost $1.10, and the total would be $1.20.
In a three-digit number, the tens digit is two more than the ones digit. The hundreds digit is one less than the tens digit. The digits add to 12. What is the number?
Call the ones digit a mystery number, then write the other two digits using it.
The hundreds digit is one more than the ones digit. Try ones digits 1, 2, 3 and add up all three digits each time.
453.
If the ones digit is 3, the tens digit is 5 (two more) and the hundreds digit is 4 (one less than 5). 4 + 5 + 3 = 12, so the number is 453. Other choices miss: a ones digit of 2 gives 342, whose digits add up to only 9.
A pen holds only chickens and rabbits. There are 20 heads and 56 legs. How many rabbits are there?
Good to know: Every chicken has 2 legs, every rabbit has 4 legs, and each animal has one head.
Every animal has one head, so there are 20 animals in all.
If all 20 were chickens, there would be 40 legs. Each rabbit has 2 more legs than a chicken.
Eight rabbits and twelve chickens.
Pretend all 20 animals are chickens: that makes 40 legs. There are 56 legs, which is 16 more. Each rabbit has 2 more legs than a chicken, so 16 ÷ 2 = 8 rabbits. The other 12 are chickens. Check: 8 × 4 + 12 × 2 = 32 + 24 = 56 legs.
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