Find the Next Number in the Sequence

2 9 3 1 8 4 3 6 5 7 ?

Replace the question mark with the correct number.

2 + 2= 4
3 + 3= 18
4 + 4= 48
5 + 5= ?

What begins with T, ends with T, and has T in it?

If EELS + MARK + BEST + WARY = EASY

What does HELP + BARK + WARD + LEAD equal?

Jack have ten pairs of black socks, eight pairs of white socks and seven pairs of green socks. Everything is mixed in a draw. As there is no light he were not able to identify the colour of the socks. How many of the socks did he want to take to match one pair

The host of a game show, offers the guest a choice of three doors. Behind one is a expensive car, but behind the other two are goats.
After you have chosen one door, he reveals one of the other two doors behind which is a goat (he wouldn't reveal a car).

Now he gives you the chance to switch to the other unrevealed door or stay at your initial choice. You will then get what is behind that door.

You cannot hear the goats from behind the doors, or in any way know which door has the prize.

Should you stay, or switch, or doesn't it matter?

If I remove one from eleven it becomes Ten and if I remove one from nine also becomes Ten. How?

What is both possible and impossible at the same time?

Double it and multiply it by 4. Then divide it by 8 and you’ll have it once more. What number is it?

Before the start of the car race, John and Jacob have the same amount of fuel in their car. With this fuel, John can drive for 4 hours while Jacob can drive five hours.
After a time they realize that the amount of fuel left in John's car is 1/4th of the fuel in Jacob's.

For how long they are racing?