I am not alive, but I grow; I don't have lungs, but I need air; I don't have a mouth, but water kills me. What am I?

What month of the year has 28 days?

What is a word made up of 4 letters, yet is also made up of 3. Sometimes is written with 9 letters, and then with 4. Rarely consists of 6, and never is written with 5.

Below is the sum of symbols in each row and column in the figure. Analyzing the figure, can you find out the value of the symbols?

If,

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

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

D + F = ?

Find the next number in the series below

21 32 54 87 131 ?

Name a key which is hardest to turn.

I am a white box having no key or lid.
Yet there is a golden treasure inside it.

What Am I?

You have to fill the below given grid in a manner that every row and column contains the digits 1 to 6. Also, make sure that the squares that are connected with each other must contains the same digit.

How many times can you subtract the number 5 from 25?