A certain street contains 100 buildings. They are numbered from 1 to 100. How many 9's are used in these numbers?

You have two strings whose only known property is that when you light one end of either string it takes exactly one hour to burn. The rate at which the strings will burn is completely random and each string is different.

How do you measure 45 minutes?

In a stable, there are men and horses. In all, there are 22 heads and 72 feet. How many men and how many horses are in the stable

Forwards I am heavy, backward I am not. What am I?

Can you find out the missing number?

? 4 5 3 5

9 5 7 10 3

Which number comes next in the number series?

2, 9, 30, 93, ?

Can you decipher these quotes by Albert Einstein?
Blf xzm mvevi hloev z kilyovn lm gsv ovevo lm dsrxs rg dzh xivzgvw.

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.

Solve the following series:
AZ, GT, MN, __, YB

What 5-letter word typed in all capital letters can be read the same upside down?