Name a key which is hardest to turn.

John has eleven friends. He has a bowl containing eleven apples. Now He wants to divide the eleven apples among his friends, in such a way that an apple should remain in his bowl.
How can He do it?

What four weights can be used to balance from 1 to 30 pounds?

Rahul decided to meet Simran so he boards a local train from Bombay station. Just after the station, there is a 1km long tunnel. The train starts and is now accelerating. Rahul is a claustrophobic guy, so what is the best position for him to sit?

When it is alive we sing, when it is dead we clap our hands. What is it?

Can it be possible to build a house that has all its four walls facing towards the South?

I am the fastest animal but cannot climb the tree. What am I?

Can you find the key in the picture below?

I am a seven-letter word but if you remove four of my letters I will have one left. What word am I?

What will be the best approach to finding all the prime numbers less than 75 that leave an odd reminder when we divide them with 5?