Correct format when talking about money \$\$

I'm writing a formal research paper (Highschool)

I have lots of statistics involving money (In fact, my whole essay is about the economy).

So a question arises about the format of writing money.

Would it be:

The company spent \$4.5 billion dollars.

or simply

The company spent \$4.5 billion.

Do I need to include the "dollars" at the end? Which one is more customary?

Thank you

• \$ and dollars are equal, hence you only need one, but the symbol would be easier for someone who is reading the paper. Commented Jun 3, 2011 at 2:44

Go with the second option. The first is redundant - you've got \$ as a symbol AND as a word.

• yes, it reads "Four point five billion dollars dollars." Commented Jun 3, 2011 at 11:55
• Also an option is "four point five billion dollars" or "4.5 billion dollars" or "4,500,000 dollars." As a sidenote, at least in MLA format any number under 1,000 is written out using words and only over 1,000 is written in digits. Of course if this is a mathematical or scientific paper different rules apply. Commented Jun 3, 2011 at 12:20
• @justkt \$4.5 billion would be \$4,500,000,000 =P Yours says \$4.5 million. Commented Jun 3, 2011 at 14:04

Depending on the context, you might wish to consider specifying which currency it is, eg

The company spent \$4.5 billion (USD)

As there are many different dollars, and they all use the same \$ symbol.

If that is the only currency used within the paper then you could state that the currency is US dollars at the start rather than for every amount.