What is both possible and impossible at the same time?

I am the one who remains awake when you sleep. But I need to rest when you awake. Who Am I?

Can you find a pattern and the missing number in the series given below?

100, 155, 258,? , 584, 819.

Can you tell a 3D object that has just two surfaces?

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

In a fruit store, there was a unique weighing machine that was made to weigh only cherries and strawberries as they were priced the same.

Other fruits like watermelons or mango had different machines as they were expensive.

A man successfully buys watermelons at the price of cherries. How?

Can you find the key in the picture below?

Count the number of lines in the image below ?

Can you find the missing letter in the sequence?
S - T - I - L - ? - T - F - Y - C

In Greek mythology, the Sphinx sat outside of Thebes and asked this riddle of all travellers who passed by. If the traveller failed to solve the riddle, then the Sphinx killed him/her. And if the traveller answered the riddle correctly, then the Sphinx would destroy herself. The riddle:

What goes on four legs in the morning, on two legs at noon, and on three legs in the evening?

Oedipus solved the riddle, and the Sphinx destroyed herself.