How is a fly different from a mosquito?

Two boys wish to cross a river. The only way to get to the other side is by boat, but that boat can only take one boy at a time. The boat cannot return on its own, there are no ropes or similar tricks, yet both boys manage to cross using the boat.

How?

Can you think of any three-dimensional shape that comprises of exactly two surfaces?

I organized a small get together at my home.
In the party , i have a barrel with some whiskey in it.

Suddenly Guest 1 say 'I bet this barrel of whiskey is more than half full'.
'No, it's less than half full' Guest 2 replied.

I don't have any measuring instrument and without removing whiskey from it , how can i determine which of the guest is right ?

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

Solve the puzzle by telling what does below picture means.

There was a man he lives in a hotel each morning he presses the first floor button each evening if there is a person in the elevator he asks him to press the 10 floor button if there is no one in the elevator he takes the stairs why.

I’m tall when I’m young, and I’m short when I’m old. What am I?

If it took eight men ten hours to build a wall, how long would it take four men to build it?

Solve below popular number sequence
314 159 265 358 979 323 846 ?