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

Speaking of rivers, a man calls his dog from the opposite side of the river. The dog crosses the river without getting wet, and without using a bridge or boat. How?

I can write cow in 13 letters.

Can You?

The first box has two white balls. The second box has two black balls. The third box has a white and a black ball.

Boxes are labeled but all labels are wrong!

You are allowed to open one box, pick one ball at random, see its colour and put it back into the box, without seeing the colour of the other ball.

How many such operations are necessary to correctly label the boxes?

If you say my name, I will no longer exist. What am I?

Can you convert the number zero(0) into a positive number using just one mathematical operator ?

Many have heard it, but nobody has ever seen it, and it will not speak back until spoken to. What is it?

An American nightclub called 'The Coconut Grove' had a terrible fire in which over 400 people died. A simple design flaw in the building led to a high death toll. Subsequently, regulations were changed to ensure that all public buildings throughout the country eliminated this one detail, which proved deadly. What was it?

What kind of band never plays music?

When I get multiplied by any number, the sum of the figures in the product is always me. What am I?