Why Aeroplane windows are round?

Take 9 from 6, 10 from 9, 50 from 40, and leave 6.

How Come ??

Which Number is the odd one out?

A) 7145
B) 2716
C) 5321
D) 4135

You have a basket containing ten apples. You have ten friends, who each desire an apple. You give each of your friends one apple.
Now all your friends have one apple each, yet there is an apple remaining in the basket.
How?

Rearrange the letters in "new door" to make one word.

Which is heavier: a ton of bricks or a ton of feathers?

One is to three as three is to five and five is to four and four is the magic number.
What is the pattern?

They do not possess flesh or feathers or scales or bone
But still, they are blessed with fingers and thumbs of their own.

Before Mount Everest was discovered, what was the highest mountain in the world?

Mr. Buttons was all set to go to the village of Buttonland to meet his friend. So, he packed his bags and left for the village at 5 in the morning. Upon travelling on a road for miles, he came across a point where the road diverged into two. He was confused on which road to take. He gazed around and he saw two owls sitting on a branch. He thought he could ask for directions for the village from the two owls. So he went to the tree. There he saw a sign which read, "One owl always lies, and one is always truthful. They both fly away if you ask them more than 1 question."
Mr. Buttons was caught in the dilemma of what to ask? And from which owl to ask, since he only had one question. What should Mr. Buttons ask?