If two's company, and three's a crowd, then whats four and five ?

If,

A + B = C
D - C = A
E - B = C

Based on the above equations, find out the answer for:

D + F = ?

What does below chemistry rebus means?

Can you solve the below geography rebus by decoding the below rebus ?

A rubber ball keeps on bouncing back to 2/3 of the height from which it is dropped. Can you calculate the fraction of its original height that the ball will bounce after it is dropped and it has bounced four times without any hindrance ?

What is the word or phrase?

Make eight squares by moving only two matchsticks.
Note- Square can be of different sizes.

What number do you get when you multiply all of the numbers on a telephone's number pad?

How many people must be gathered together in a room, before you can be certain that there is a greater than 50/50 chance that at least two of them have the same birthday?

As a whole I am both
safe and secure.

Behead me and I become
a place of meeting.

Behead me again and I am
the partner of ready.

Restore me, and I become
the domain of beasts.

What am I?