What do you answer even though it never asks you questions?

If,

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

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

D + F = ?

When it is alive we sing, when it is dead we clap our hands. What is it?

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 ?

why number 8549176320 is one of a kind?

Spot the cat in the picture below

A girl rode into a tourist spot out of the city on Thursday. She loved the place and decided to stay for a few days. She stayed for four days and then she left for back home on Thursday.

How can this be possible?

It walks on 4 when its young, walks on 2 when it's older, and walks on 3 when its very old?

Find the missing number in the image below.

I have an eye but still cannot see.

Who am I?