Why Aeroplane windows are round?

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?

What English word has three consecutive double letters?

If you toss a coin 10 times and it lands heads up every time, what are the chances it will land heads up if you toss it again?

I am taken from a mine and shut up in a wooden case, from which I am never released, and yet I am used by almost every person. What am I?

I am an odd number. Take away a letter and I become even. What number am I?

If nine thousand, nine hundred nine dollars is written as $9,909,
how should twelve thousand, twelve hundred twelve dollars be written?

Rectify the following equality 101 - 102 = 1 by moving just one digit.

What will you call your mother's brother's brother-in-law?

Can you name any English verb that becomes its past tense by simply rearranging the alphabets ?