Which number should replace the question mark?

There are three light switches outside a room. One of the switches is connected to a light bulb inside the room.
Each of the three switches can be either 'ON' or 'OFF'.

You are allowed to set each switch the way you want it and then enter the room(note: you can enter the room only once)

Your task is to then determine which switch controls the bulb?

The pound is not a finish.

We are sharing a few instructions below, which you have to use in any suitable order to modify the above sentence such that the end sentence is a scientific fact.

- Eliminate a letter and supplement another in its place.
- Take away one word.
- Remove one letter from one word.
- Get rid of two letters from one word.
- Swap a word with its antonym.

How can you take 2 from 5 and leave 4?

Two friends were stuck in a cottage. They had nothing to do and thus they started playing cards. Suddenly the power went off and Friend 1 inverted the position of 15 cards in the normal deck of 52 cards and shuffled it. Now he asked Friend 2 to divide the cards into two piles (need not be equal) with equal number of cards facing up. The room was quite dark and Friend 2 could not see the cards. He thinks for a while and then divides the cards in two piles.

On checking, the count of cards facing up is same in both the piles. How could Friend 2 have done it ?

The measurement of time, That can't be found on a clock, But can be looked upon on a map.

Who is He ?

A Doctor always sneezes before the rain. Doctor sneezes, Will it rain?

Irene killed hundreds of people mercilessly and yet the police were not able to put her behind the bars. Why?

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?

You’ll find me on Mercury, Earth, Mars, Jupiter, Saturn, and Uranus. But never Neptune, or Venus. What am I?