What is the fastest way to double your money?

If nine thousand, nine hundred nine dollars is written as $9,909,
how should twelve thousand, twelve hundred twelve dollars be written?

You are in a room that has three switches and a closed door. The switches control three light bulbs on the other side of the door. Once you open the door, you may never touch the switches again. How can you definitively tell which switch is connected to each of the light bulbs?

Find The Next Number In The Sequence

30 10 15 13 0 16 -15 ?

A thief enters a store and threatens the clerk, forcing her to open the safe. The clerk says, “The code for the safe is different every day, and if you hurt me you’ll never get the code.” But the thief manages to guess the code on his own. How did he do it?

I am sure no one can have two things for dinner. what are they?

I have cities, but no houses. I have mountains, but no trees. I have water, but no fish. What am I?

What does below Rebus say?

XLR8

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?

One night, a woman receives a call from the police. They tell her that her husband was murdered and that she should come to the crime scene as soon as possible. The woman drops the phone, shocked, and drives 20 minutes to the crime scene. As soon as she reaches the crime scene, the police arrest her and she is convicted of murder. How do the police know she committed the crime?