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.

If 24H in a D => 24 hours in a day.
What does "64S on CB" stand for?

What does below chemistry rebus means?

A word I know,
Six letters contain,
Subtract just one,
And twelve is what remains.

Four men were in a boat on the lake. The boat turns over, and all four men sink to the bottom of the lake, yet not a single man got wet! Why?

I look flat, but I am deep. Hidden realms I shelter. Lives I take, but the food I offer. At times I am beautiful. I can be calm, angry, and turbulent. I have no heart but offer pleasure as well as death. No man can own me, yet I encompass what all men must have. What am I?

I can be cracked, made, told, and played. What am I?

What does this rebus puzzle mean?

What is the centre of gravity?

Can you count the number of rectangles on a chessboard?