Because these types of quantity indicators are usually used in singular according to grammar rules. These are imagined as singular although it's not so. For ex: -- 2000 metres is very difficult to run in 10 minutes.

Because these types of quantity indicators are usually used in singular according to grammar rules. These are imagined as singular although it's not so. For ex: -- 2000 metres is very difficult to run in 10 minutes.

It's used as a singular noun because you are thinking of it as one amount rather than individual pieces of money.

Even though $50 can made up of several smaller denominations, it is thought of as one bunch or one amount when used this way in a sentence. You are thinking of the amount rather than individual bills.

I was He was She was It was You were We were They were 50.00 is a thing that why is : was no were