Jim types 70 words per minute. today, he sat at his computer to finish a document he had started yesterday. after jim typed for 3 minutes, the document had a total of 400 words. how many words were already in the document before jim opened it today?

There was 200 words before Jim opens the document and started typing.

If Jim gets 70 words done in 1 minute and he just typed a document for 3 minutes, you would do 70 * 3 to find out how much he typed in 3 minutes. So he typed 210 words in 3 minutes.

Then, since he ended off with 400 words, you would do 400 - 210 to find out how much words were already in the document before he opened it and started typing.

So Jim typed 210 words in 3 minutes.

And there was 290 words before Jim started typing.

Correct me if I'm wrong.

190 words is the answer