Find out the missing number in the picture attached:

What has one letter and starts with an E?

Our product and our sum always give the same answer. Who are we?

A man died and leaves Rs.10,000 in his will. There are 6 beneficiaries- his 3 sons and their wives. The 3 wives receive Rs.3960 of which Priyanka gets Rs.100 more than Tanu and Neha gets Rs.100 more than Priyanka.
Pramod gets twice as much as his wife, Tushar gets the same as his wife, and Prashant gets 50% more than his wife.

Who is married to whom?

Two friends Smith and Andrew were talking about the bravery of their families. Smith told great stories about his courageous grandfather who fought for Britain in "World War I". Andrew told that his grandfather was so brave that in 1919 just after the war he was honoured with a bravery medal with the words "For our Courageous Soldiers In World War I" embedded into it. Smith knows that his friend is lying. How?

Can you think of any three-dimensional shape that comprises of exactly two surfaces?

John left on a horse on Thursday , was gone for two days, and came back on Thursday after completing his work. How did that happen?

Can you place six X (crosses) in below board without making three in a row in any way ?

A finger goes in me. You fiddle with me when you're bored. The best man always has me first. What am I?

I have no doors but I have keys, I have no rooms but I have space, you can enter but you can’t leave! What am I?