Replace the question mark with the number below given a simple math problem.

When can we add 2 to 11 and get 1 as the correct answer?

There is a square of a particular number which when doubled, becomes 7 more than its quarter.

Can you find the number?

What am I?

Which alphabet is a part of our body?

What has 88 keys?

Prove that twice of ten is the same as twice of eleven.

Find The Missing Number In the Sequence.
6 25 64 ? 32 1

If in a code language, DISTANCE is written as IDTUBECN and DOCUMENT is written as ODDVNTNE, the how will THURSDAY be coded as in the same language?

10 people came into a hotel with 9 rooms and each guest wanted his own room. The bellboy solved this problem.
He asked the tenth guest to wait for a little with the first guest in room number 1. So in the first room, there were two people. The bellboy took the third guest to room number 2, the fourth to number 3, ..., and the ninth guest to room number 8. Then he returned to room number 1 and took the tenth guest to room number 9, still vacant.
How can everybody have his own room?