Can you arrange four 9's and use at most 2 math symbols, to make the total 100?

You have a three-gallon and a five-gallon measuring device. You wish to measure out four gallons.

Your last good ping-pong ball fell into a narrow metal pipe embedded one foot deep in concrete.
How can you get it out undamaged, if all the tools you have are your tennis paddle, shoe laces, and plastic water bottle, which does not fit into the pipe?

What goes through cities and fields, but never moves?

A wooden log balances equally on the scales when weighed with three-quarters of a pound and three-quarters of a wooden log.

Can you calculate the weight of the entire wooden log?

Prove that twice of ten is the same as twice of eleven.

I am lying and I always lie. Tell me whether I am lying or telling the truth.

Solve the puzzle by telling what does below picture means.

I had an infinite supply of water and 5 litres and 3 litres jars.

How would you measure exactly 4 litres in the least number of steps?

How is a fly different from a mosquito?