Why 1729 is a magic number? Answer Logically.

What does this rebus mean?

O
N
C
E
TIME

If,

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

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

D + F = ?

What does the below mathematical rebus mean?

When you say goodbye, I am what you need to tie.
I come as a couple and go wherever you run.
Who am I?

You have two strings whose only known property is that when you light one end of either string it takes exactly one hour to burn. The rate at which the strings will burn is completely random and each string is different. How do you measure 45 minutes?

Once while in his court, King Akbar asked Birbal to write something on a wall that makes one sad when read in good times and makes one happy when read in sad times.

He took only a few moment and wrote something that fit the requirements. What did he write?

What happened when the wheel was invented?

If six children and two dogs were under an umbrella, how come none of them got wet?

Can you find out the missing number in the grid?