Prepositions with dates and numbers

Do not use different constructions in the same sentence. "The First World War was from 1914 to 1918" and "The First World War was between 1914 and 1918" are both correct. Do not say "between 1914 to 1918."

You can also just use the numbers with a hyphen, as in "1914-1918". (Though this is a common form to save space in reference books, it is not really acceptable in formal academic writing.) Again, do not mix two constructions: "from 1914-1918" is wrong.

The same applies to any other numbers used to give the outside limits of a range. "The company expects to make profits of £10-15 million (OR 'of between £10 million and £15 million' OR 'from £10 to £15 million')." This should never be "of between £10 million to £15 million."

The way in which we use words to talk about large numbers is quite variable in English. In academic writing, I would repeat as much as is necessary of the number to avoid ambiguity. For example, "£10 million to £15 million" is unambiguous, if rather repetitious and boring. "£10 to £15 million" might mean "£10 < x < £15 000 000", which is probably not what the writer meant, or "£10 000 000 < x < £15 000 000".

See also dates.