I have no doors but I have keys, I have no rooms but I have space, you can enter but you can’t leave! What am I?

Can you circle exactly four of these numbers such that the total is twelve?

1 6 1
6 1 6
1 6 1
6 1 6

O_er_t_o_

Complete the missing letters of the given word.

What does it mean?

A pond had 60 fish, out of which, all but 20 died.
How many fishes are now present in that pond?

Three doctors said that Bill was their brother. Bill says he has no brothers. How many brothers does Bill actually have?

No one wants to have it, but if one got it, he does not want to lose it. What is It?

I can be cracked, made, told, and played. What am I?

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

Two boys wish to cross a river. The only way to get to the other side is by boat, but that boat can only take one boy at a time. The boat cannot return on its own, there are no ropes or similar tricks, yet both boys manage to cross using the boat.

How?