SOLUTION: David Leaves home for his school at a speed of 12 mph. Twenty minutes later his father starts following him at a rate of 36 mph. How long(in minutes) will the father take to catch

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Question 1066545: David Leaves home for his school at a speed of 12 mph. Twenty minutes later his father starts following him at a rate of 36 mph. How long(in minutes) will the father take to catch up with David?
Answer by ikleyn(52805) About Me  (Show Source):
You can put this solution on YOUR website!
.
4%2F%2836-12%29 = 4%2F24 = 1%2F6 hour = 10 minutes.

4 is 4 miles = 12 mph * 1%2F3 hour.
It is the distance for David be ahead at the moment the father started his move.

36 - 24 in the denominator is the relative speed.