You may enter, but you may not come in. I have space, but no room. I have keys, but open no lock. What am I?

Can you arrange four 9's and use at most 2 math symbols, to make the total 100?

John is the son of Jacob.
So,
Jacob is the_____of John's father?

Find the last number in the series below:

voN luJ yaM raM ---

Two girls were born to the same mother, on the same day, at the same time, in the same month and year and yet they're not twins. How can this be ?

Two guards were guarding the camp.Guard-1 was looking towards the south to make sure no threat is coming from the road.Guard-2 was looking at the north to make sure no threat is coming from the top. Suddenly Guard-1 ask the Guard-2 why he is smiling?How Guard-1 knows that Guard-2 is smiling?

Imagine you are in a room with no windows or doors. How will you get out?

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

When I got four, I have it none.
When I got two, I have it some.
When I got none, I have it all.

What is it?

Name a key which is hardest to turn.