What goes up but never comes down?

Four men were in a boat on the lake. The boat turns over, and all four men sink to the bottom of the lake, yet not a single man got wet! Why?

Find a 9-digit number, which you will gradually round off starting with units, then tenth, hundred etc., until you get to the last numeral, which you do not round off. The rounding alternates (up, down, up ...). After rounding off 8 times, the final number is 500000000. The original number is commensurable by 6 and 7, all the numbers from 1 to 9 are used, and after rounding four times the sum of the not-rounded numerals equals 24.

Can you find out the missing number?

? 4 5 3 5

9 5 7 10 3

How could a baby fall out of a twenty-story building onto the ground and live?

Can you think of any three-dimensional shape that comprises of exactly two surfaces?

A mother bought three dress for her triplets daughters(one for each) and put the dresses in the dark. One by one the girls come and pick a dress.
What is the probability that no girl will choose her own dress?

If you’ve got me, you want to share me; if you share me, you haven’t kept me. What am I?

I have holes on the top and bottom. I have holes on my left and on my right. And I have holes in the middle, yet I still hold water. What am I?

Prove that the below maths equation is true.

8 + 8 = 91