Look at this sequence from top to bottom. What is the next number in the sequence?
1
11
21
1211
111221
312211

What is the four-digit number in which the first digit is one-third the second, the third is the sum of the first two, and the last is three times the second?

There are 2 sand hourglasses.

The small one can measure 5 hours and the large one can measure 7 hours.

How can we measure 16 hours with 2 sand hourglasses running together ?

You have to put a letter on the following to make it a meaningful word. The only challenge is that you can't use 'E'.

S E Q U E N C _

You are given a cube that is made with the help of 10x10x10 smaller cubes summing up to a total of 1000 smaller cubes. You are asked to take off one layer of the cubes.
How many remain now?

Replace the question mark with the correct number.

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

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

What 4-letter word can be written forward, backward or upside down, and can still be read from left to right?

How can you write nineteen in a manner that if we take out one, it becomes twenty?

I have an eye but still cannot see.

Who am I?