Why Aeroplane windows are round?

It's pretty hard to give up.
If you remove a part of it, you will be left with a bit.
Even if you remove another part, the bit still remains.
Remove one more and it still remains.

What is it?

A mile-long train is moving at sixty miles an hour when it reaches a mile-long tunnel. How long does it take the entire train to pass through the tunnel?

A man has a barrel filled with oil that weighs 100 pounds, and then he puts something into it. Now the barrel weighs less than 100 pounds. What did he put in the barrel?

You need to pick one entry from pot A and one from pot B to have a perfect match. Can you do it?

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

How many words can a pen with half refill write?

What month of the year has 28 days?

Can you count the number of triangles in the given picture?

Use only one mathematical symbol and all numbers (0-9) to get a sum of 99