Question

Mr. Anders and Ms. Rich each drove from a business meeting. Mr. Anders traveled east at 100 kilometers per hour and Ms. Rich traveled west at 80 kilometers per hours. In how many hours were they 100 kilometers apart.

Answer 1

If you counted up until they were 100 kilometers apart it would look like this:
Mr. A - 100, 200, 300, 400, 500
Ms. R - 80, 160, 240, 320, 400

They were 100 kilometers apart in 5 hours.