Find the next number in the sequence

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

You can find some missing letters in the picture. By placing two particular letters in the spaces, you can form a nine lettered word beginning from one of the corners and going clockwise direction to the middle. Can you find out the letters and the word?

When is the top of a mountain similar to a savings account?

Can you figure out the logic I used to decide the order of the following words:
gun, shoe, spree, door, hive, kicks, heaven, gate, line, den

Can you decipher the following common phrase?

T M C
A U O
H S M
W T E

How many times can you subtract the number 5 from 25?

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

How many pluses should we put between the digits of 987654321 to get a total of 99, and where?

John left on a horse on Thursday , was gone for two days, and came back on Thursday after completing his work. How did that happen?

Until it is measured, not known. Yet how you miss it when it has gone. What is it?