If 5 cats catch 5 mice in 5 minutes, how long will it take one cat to catch a mouse?

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

If in a car race, the man who came two places in front of the last man finished one ahead of the man who came fifth, how many contestants were there?

Using four sevens (7) and a one (1) create the number 100. Except for the five numerals, you can use the usual mathematical operations (+, -, x, :), root and brackets ()

A tree doubled in height each year until it reached its maximum height over the course of ten years. How many years did it take for the tree to reach half its maximum height?

A man is walking down a road with a basket of eggs. As he
is walking he meets someone who buys one-half of his eggs
plus one-half of an egg.
He walks a little further and meets another person who buys
one-half of his eggs plus one-half of an egg.
After proceeding further he meets another person who buys
one-half of his eggs plus one half an egg. At this point, he
has sold all of his eggs, and he never broke an egg.
How many eggs did the man have to start with?

A 52% bias toss for head using the 51% tail bias coin was done to obtain a fair result.

Can you find how bias is the floor in this case?

There are two candles. Both will only burn exactly for an hour. How will you use these two candles to measure forty-five minutes?

Christina has four daughters, and each of her daughters has a brother. How many children does Christina have?