What has no start, end, or centre?

A man has eighty-one cows ( numbered 1,2,3...81 as such). The beauty is that cow no. 1 gives 1ltr of milk, cow no. 2 gives 2ltrs of milk and so on. The man wants to equally distribute the cows among his nine sons so that each one of them gets the same quantity of milk.

There are 2 people near the river and both of them want to get on the other side. The boat can only take one of them. But they got across.
How?

Until it is measured, not known. Yet how you miss it when it has gone. What is it?

If your uncle’s sister is not your aunt, what relation is she to you?

Find the number of squares in the below picture

You can win me and lose me but never buy me
You can not eat me and never want to part with me
I can make you cry or bring you joy
I am not a machine and definitely not a toy
You keep me but i am not forever just yours
You might find me in a case or on a shelf next to a vase
I am hard and i am tall if you bump me i am sure to fall
I am made of different materials and am at many events
If your lucky and fight hard I might be yours
What am I ?

A woman lives in a skyscraper thirty-six floors high and is served by several elevators which stop at each floor going up and down. Each morning she leaves her apartment and goes to one of the elevators. Whichever one she takes is three times more likely to be going up than down. Why?

How many times can you subtract the number two from the number fifty?

I am a seven-letter word but if you remove four of my letters I will have one left. What word am I?