Which number should replace the question mark?

Can you count the number of rectangles on a chessboard?

John is selling fruits.
He sells grapes at $30, Dates $25, and a Wolfberry $45.
At what price does he sell fig?

PS: Logical Thinking

Three friends named Mr. Black, Mr. Yellow and Mr. Green enter a pub on a weekend night. They are wearing either a Black, Yellow or Green shirt.

Mr. Yellow says to them, 'Did you notice that we all are wearing different color shirts than our names?'

To this, the man who was wearing the Green shirt said. 'Wow, thats right.'

Can you identify who is wearing which colour shirt ?

How can one talk without saying a single word?

Can you think of a smallest +ve number such that if we shuffle the digits of the number, the new number becomes double the original number?

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.

When does a USA Potato change its nationality?

Keyboard words are not in alphabetical order, Why?

Take away the whole and some still remain. What is it?