Hard Riddles for Kids

They are a grandfather, his son, and his grandson.

The grandfather is a father. His son is a father too, because he has a son of his own, and he is also a son. The grandson is a son. That makes two fathers and two sons, but only three people, so three sandwiches are enough.

Second place.

To pass the runner in second place, you must be right behind them, in third place. When you pass, you take their spot: now you are second, and they are third. The runner in first place is still ahead of you, so the quick answer "first" is not right.

Two.

Many people answer three, because three apples are left on the table. But the question asks how many apples you took, and you took two.

The blue box.

The ball must be in one of the three boxes. It is not in the red box, and it is not in the green box, so the only box left is the blue one.

No.

Every red block is a cube, and no cube can roll. So every red block is a cube that cannot roll. In real life you might tip a cube over, but inside this pretend game the rules are always true.

Bo.

Ali is ahead of Bo, and Bo is ahead of Cam. So from the front, the line goes Ali, Bo, Cam, and Bo is in the middle.

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.

Thursday.

Count three days forward from Monday: Tuesday is one, Wednesday is two, and Thursday is three.

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.

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.

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.

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 quarter and a nickel. The quarter is the one that is not a nickel.

The only two US coins that make 30 cents are a quarter (25 cents) and a nickel (5 cents). The riddle says one of them is not a nickel, and that is true: the quarter is not a nickel. The other coin is.

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.

Take the chicken across. Go back alone. Take the fox across. Bring the chicken back. Take the grain across. Go back alone. Take the chicken across.

The chicken is the problem: it cannot be left with the fox or with the grain, so it crosses first. Then the farmer takes the fox over, brings the chicken back, swaps it for the grain, and fetches the chicken last. Taking the grain before the fox works too. Seven trips is the fewest possible.

Anna has the fish, Beth has the cat, and Cara has the dog.

Anna has neither the cat nor the dog, so she has the fish. Beth does not have the dog, and the fish is taken, so Beth has the cat. That leaves the dog for Cara.

Weigh three against three. If they balance, weigh the last two against each other. If one side is heavier, take two balls from that side and weigh one against the other; if they balance, the third ball from that side is the heavy one.

Weighing 3 against 3 splits the eight balls into three groups: one pan, the other pan, and the 2 set aside. If the scale balances, the heavy ball is one of the 2 set aside, and one more weighing finds it. If one side is heavier, the heavy ball is one of those 3: weigh 1 against 1, and if they balance, it is the third. Either way, two weighings are enough.

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.

Three.

The first two socks might not match: one red and one blue. The third sock has to be red or blue, so it always matches one of them. Three socks are always enough, and two are not.

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.