When can we add 2 to 11 and get 1 as the correct answer?

I have Rs.50 and I spend it in the way as below.

I make a loud sound when I’m changing. When I do change, I get bigger but weigh less. What am I?

A Scientist was fifty years old in the year 2000 but he was forty years old in the year 2010. How can this be possible?

PS: It has a logical answer.

A sea diver is a real show-off. He showed everyone that he can hold his breath underwater for 15 minutes.

I went to the diver and told him that I can be underwater for double the time i.e 30 minutes.
He responded that he will give me 100$ if I would be able to do it. I won 100$.

What did I do?

I don't get anymore wetter, no matter how much rain falls on me.

Find the number of squares in the below-given picture.

Why do you find that most of the buildings are deprived of the 13th floor?

It's a test that will check your IQ.

Suppose you have one 11 minute hourglass and one 13 minute hourglass.

Can you measure exactly fifteen minutes using them ?

Count the number of squares in the picture below.