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

What is black when you buy it, red when you use it, and gray when you throw it away?

The UN Security Council has how many member states?

a) 15
b) 10
c) 20
d) 25

If you remove one from eleven, it becomes ten. If you remove one from nine, it becomes ten.

How is this possible?

Always in you, Sometimes on you;

If I surround you, I can kill you.

What am I?

John was running from 40 thieves. John has got 3 gold boxes which weigh as 4kg, 2kg, and 1kg respectively. A witty man asked John to stay with him for seven days in exchange for 1kg gold per day. John needs to stay there for seven days and also do not want to give the witty man any advance. How can John pay for his seven days stay?

You are offered an opportunity to win a fortune. There are 100 precious black stones and 100 unworthy white stones. There are two different sacks labelled as "Heads" and "Tails". You can distribute the stones as you wish. Then a coin will be flipped. Then you will have to choose a stone from the corresponding sack. If you pick up a black stone, all the fortune of black stones is yours but if you pick up white, you get nothing.

How will you distribute the stones so that you can maximize your chances of winning?

What is the next number in this series?

4,12,84,3612....

What kind of storm is always in a rush?

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 ?