Can you make four (4) nines (9) equal 100?

In the picture given below, can you find out which digit will take place of the question mark?

Identify the next two numbers in this series.

101, 112, 131, 415, 161, 718, ???, ???

What is the centre of gravity?

You walk into an old horror house. It has no power or plumbing. Once inside, you see three doors. Each door has a number on it. Behind each door is a way for you to die. Behind door number one, you die by getting eaten by a lion. Behind door number two, you die by getting murdered. Behind door number three, you die by an electric chair. You can’t turn back, so you have to go through a door. Which door do you go through?

How many letters are in the alphabet?

Can you find out which number multiplied by itself will give the output as 12345678987654321?

I am quite hot but become too cold if you remove the first two letters. What am I?

You have a roll of cloth 1km long. You have a machine which cuts this roll into pieces of 10-meter-long cloth.

How long would it take for the machine to cut the roll if each cut took 4 secs?

Can you find out the number that should replace the question mark with a valid reason?