rain-Teasers

Easy

1. screwy pirates (分割100coin）

2.Tiger-Sheep

1. River cross

4.birthday : only know month, only know day

5.cards game: black and white discard, double black to delader, white to yours

1. boring ropes

2. x^x^x…

3. calendar cube

4. prove dividable by 9,11,3

5. clock broke into 3 pieces

6. missing integer in a series

7. counterfeit coins (10 bag, 100 coins one different bag)

8. matching socks

9. share hands

10. 6 people, 3 people shake hands

11. ants on a square (to cover)

Medium

1. how many trailing zeros in 100! 1000！ 10000！

2. park 53 bricks of 1*1*4 in a 6,6,6 box

3. Turn over Glass- 50 wisemen communicate once

4. Glass balls, 100 stairs, 2 balls larger than X breaks, how to try?

   what if 3 balls？

5. chameleon: meet each other, change color

6. coin split to two piles, add, two piles add

7. chocolate bar

8. counterfeit coins 2- 5 bags with 100 (m) coins, n possible weight

9. One step or two step, how many ways to go up a hundred stairs (Fibonacci)

   • extension: one or two or three steps, how many ways

Hard

1. weight 8,12,13,90,144 balls

2. race 25 horses

3. light switch 4 switch 1 light

4. coin piles 20 heads, 980 tail-two piles with same heads, can turn over but cannot see

5. prisoner with colored heads, communicate once, guess hat

6. 7 hats color, guess to ensure at least one right

7. race track (race wrong a circle)

8. proof irrational number

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