What's the only room from which no one can enter or leave

Find The Next Number in the series:

12 13 15 17 111 113 117 119 123 ?

Can you divide numbers from 1 to 9 (1 2 3 4 5 6 7 8 9) into two groups so that the sum of the numbers of each group is equal?

Note: 9 cannot be turned over to make it 6.

Rearrange the letters in "new door" to make one word.

Find the 8 in the below-given Image.

what does this picture(rebus) riddle means ?

There are people and strange monkeys on this island, and you can not tell who is who (Edit: until you understand what they said - see below). They speak either only the truth or only lies.
Who are the following two guys?
A: B is a lying monkey. I am human.
B: A is telling the truth.

Why do you find that most of the buildings are deprived of the 13th floor?

Who always enjoys poor health?

If,
9 * 8 * 7 = 65
8 * 7 * 6 = 50
7 * 6 * 5 = 37

Find
6 * 5 * 4 = ?