I am white when I am dirty, and black when I am clean. What am I?

A mother is 21 years older than her child. In exactly 6 years from now, the mother will be exactly 5 times as old as the child.
Where's the father?

What can go through glass without breaking it?

'S' refers to the number of seconds in a day and 'H' refers to the number of hours in ten years. Which quantity out of these two is greater?

Can you find out the missing number?

? 4 5 3 5

9 5 7 10 3

If eleven plus two equals one, what does nine plus five equal?

Can you find the largest Three-digit number whose sum is 14 and whose square is less than 5,00,000?

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

I know there are two methods by using three time the same number with a plus(+) operator , you can make sum as 60.

One of them is 20+20+20.

whats the other way ?

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.