An mount of something is how much there is. Amount of is used especially for something that cannot be counted or measured. It is followed by a single noun. For example we cannot say an amount of people/shops/problems because these nouns are countable.
- A huge amount of information can be stored in a computer's memory.
- The company spent a large amount of money on advertising.
- They put a considerable amount of effort and time into this project.
A quantity is an amount of something that can be counted or measured. A quantity of can be followed by a single noun or a plural noun. It is used with inanimate objects.
- The police found a small quantity of drugs in his apartment.
- They consumed a large quantity of alcohol at the party.
- Our country is exporting sufficient quantities of wheat.
Be careful not to confuse quantity with quality [=how good or bad something is].
- It's not the quantity, but the quality that matters.
- The quantity and quality of raw materials were controlled.
We use number of to indicate a quantity of people or things. Number of is used with plural nouns.
After the number of we use a single verb.
- A large number of people attended the march.
- The number of people living in extreme poverty has increased substantially.
- A number of students have volunteered to help children.
a huge/large/significant/vast amount of something
a limited/small/tiny amount of something
a large/small/tiny quantity of something
enormous/vast/huge quantities of something
a large/small number of someone/something