You have driven the first 10 miles of a 20 mile trip at an average speed of 25 miles per hour. How fast would you have to go in the second half of your trip to average 40 miles per hour over the entire distance?
Answer:
100 miles per hour .......... Using the formula D = RT, it has taken you 24 minutes to drive the first ten miles (10 = 25 T, T = 10/25 or 2/5 hr. = 2/5 x 60 = 24). To average 40 mph over 20 miles would take 30 minutes (20 = 40 T). Therefore you have 6 minutes to drive the remaining 10 miles. 6 minutes is 1/10 of an hour. So 10 = R 1/10, R =100.
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