Vietnamese students usually feel confused when talking about cardinal numbers. I hope this part will help you overcome this weakness.
Separation between hundreds and tens
Hundreds and tens are usually separated by 'and' (in American English 'and' is not necessary).
110 - one hundred and ten1,250 - one thousand, two hundred and fifty2,001 - two thousand and one
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 hundred2,100 - two thousand, one hundred
Thousands and Millions
Use 1,000 and 1,000,000 always with 'a' or 'one'.
1,000 - a thousand / one thousand201,000 - two hundred and one thousand
Use commas as a separator.
The Number 1,000,000,000
In English this number is a billion. This is very tricky for nations where 'a billion' has 12 zeros. 1,000,000,000,000 in English, however, is a trillion.
But don't worry, these numbers are even a bit problematic for native speakers: for a long time the British 'billion' had 12 zeros (a number with 9 zeros was called 'a thousand million'). Now, however, also in British English 'a billion' has 9 zeros. But from time to time this number still causes confusion (just like this paragraph, I'm afraid). ;o)
Singular or Plural?
Numbers are usually written in singular.
two hundred Eurosseveral 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 Eurosthousands of light years