Numbers

Separation between hundreds and tens

Hundreds and tens are usually separated by 'and' (in American English 'and' is not necessary).

110 - one hundred and ten
1,250 - one thousand, two hundred and fifty
2,001 - two thousand and one

Hundreds

Use 100 always with 'a' or 'one'.

100 - a hundred / one hundred

'a' can only stand at the beginning of a number.

100 - a hundred / one hundred
2,100 - two thousand, one hundred

Thousands and Millions

Use 1,000 and 1,000,000 always with 'a' or 'one'.

1,000 - a thousand / one thousand
201,000 - two hundred and one thousand

Use commas as a separator.

57,458,302

Singular or Plural?

Numbers are usually written in singular.

two hundred Euros
several thousand light years

The plural is only used with dozen, hundred, thousand, million, billion, if they are not modified by another number or expression (e.g. a few / several).

hundreds of Euros
thousands of light years

</