If two typists can type two pages in five minutes, how many typists will take it to type twenty pages in ten minutes?

None of these

Let's break it down:

2 typists can type 2 pages in 5 minutes, so:

2 typists can type 4 pages in 10 minutes.

To type 20 pages in 10 minutes, we'll need:

20 pages / 4 pages = 5 times more typists

Since 2 typists can type 4 pages, we'll need:

2 typists × 5 = 10 typists