Which number should replace the question mark?

What is the fastest way to double your money?

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

A man plots the murder of his wife. His plan is full proof. Nobody saw them leaving their house. He stabbed her with a knife while driving. She died on the spot. He threw her body in a valley. He threw the knife carefully wiping his finger prints on a random garbage bin. Then he went back to his home and no one was watching him this time as well.

After an hour, he was called by the local police department who informed him that his wife was murdered. They asked him to reach the scene of crime immediately. But as soon as he arrived at the crime scene, he was arrested by them.

How did the police know that he himself is the murderer?

Where do fish keep their money?

Can you replace the question mark with the correct number in the below table sequence?

Many have heard it, but nobody has ever seen it, and it will not speak back until spoken to. What is it?

Two guards were guarding the camp.Guard-1 was looking towards the south to make sure no threat is coming from the road.Guard-2 was looking at the north to make sure no threat is coming from the top. Suddenly Guard-1 ask the Guard-2 why he is smiling?How Guard-1 knows that Guard-2 is smiling?

Can you find the next number in the below sequence
3 , 7 , 10 , 11 , 12 , 17 ?

Spelt forwards I’m what you do every day, spelled backwards I’m something you hate. What am I?