What does below rebus means ?

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

1, 2, 6, 21, 88, __?

Luis Garavito killed Density x Volume.

Who is Luis Garavito ?

There is an English word that can be used up to four times in a row without modifying the spelling and form a valid grammatical sentence.

Do you know what word is that?

Living above a star, I do not burn
Eleven friends and they do not turn
I can just be visited in a sequence, not once or repeatedly
PQRS are my initials
Can you tell my name accurately?

With the help clues provided in the image, can you find the 5 digit key?

Look at this sequence from top to bottom. What is the next number in the sequence?
1
11
21
1211
111221
312211

If "P" means "-", "Q" means "/", "R" means "+", and "S" means "*" then find the value of the following:

21 Q 7 R 9 S 10 P 13

Name one eight-letter word with 'kst' in the middle, 'in' the beginning, 'and' at the end.?