Can you solve this amazing hard number series problem?
7, 8, 10, 12, 16, 18 ?

There are 20 people in an empty, square room. Each person has full sight of the entire room and everyone in it without turning his head or body, or moving in any way (other than the eyes). Where can you place an apple so that all but one person can see it?

Can you find the missing letter in the sequence?
S - T - I - L - ? - T - F - Y - C

What have one eye but still cannot see?

Keyboard words are not in alphabetical order, Why?

Two in a corner, one in a room, zero in a house, but one in a shelter. What am I?

Always in you, Sometimes on you;

If I surround you, I can kill you.

What am I?

What can go up a chimney down, but can’t go down a chimney up?

_ _ _ IE _ _
_ _ _ IE _
_ _ IE _ _
_ _ IE _
_ _ _ _ IE

Like you see, some letters have gone missing from these words that contain the IE pair at some or the other place. The letters that will be used to fill the blanks are given below. Use them and form meaningful words. Can you do that?

A, C, D, F, H, K, L, M, N, N, O, R, R, S, S, S, T, T, Y and Y.

What is in seasons, seconds, centuries and minutes but not in decades, years or days?