If it took eight men ten hours to build a wall, how long would it take four men to build it?

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.

Two-person want to cross a river. Only one boat is present on the riverside that can carry only one person at a time.

However, they still manage to cross the river. How is it possible?

If 5 cats catch 5 mice in 5 minutes, how long will it take one cat to catch a mouse?

Rectify the following equality 101 - 102 = 1 by moving just one digit.

My friends called me Iron59 because my parents are a chemist and a mathematician. What is my real name?

Only one colour, but not one size,
Stuck at the bottom, yet easily flies.
Present in sun, but not in rain,
Doing no harm, and feeling no pain.
What is it?

Solve the equation by replacing the alphabet with numbers.

MOM + MOM + NO = BOOK=

What is the coolest letter in the alphabet?

Our product and our sum always give the same answer. Who are we?