Question

You started on a bike trip, riding at a rate of 9 miles per hour. Your friend left one hour later and rode at the rate of 12 miles per hour. How long did it take your friend to catch up with you?

Answer 1

You're 9 miles ahead when the 2nd bike starts.
His speed wrt you is 3 mph (12-9).
9/3 = 3 hours
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