What is the fastest way to double your money?

There is a shop where written:
Buy 1 for $1
10 for $2
100 for $3
I needed 999 and still only paid $3. How could this be financially viable for the shop-keeper?

What is both possible and impossible at the same time?

Forwards I am heavy, backward I am not. What am I?

The more you take me, the more you leave me behind.
Who Am I?

Shyla was sleeping in her apartment when suddenly a robber broke into her house. He asked her to stay quiet and started looting the cash and jewelry. Suddenly the landline phone started ringing. The robber pointed a gun at Shyla and asked her to pick up and talk without giving away the situation.

She picked up the phone and it happened to be her husband. She spoke, Is it an emergency darling? Do give me a call when your flight lands, I will prepare your favorite food that will help you relieve the stress. Then she hanged up.

10 minutes after, the police arrive at the scene and catch the robber. How did the police know about the robbery?

In one of the popular batman series movie "Batman Forever", there was a riddle that goes like "Tear me off and then scratch my head and I was red then and now I am back. Who am I?

What can run but never walk, have a mouth that never speaks, have a head that never weeps, and have a bed but never sleeps?

What does this below rebus puzzle mean?

Find The Next Number In The Sequence

30 10 15 13 0 16 -15 ?