SOLUTION: Helen drives from her house to a store at 25 mph. She drives back along the same route at 35 mph. When she gets home she realizes she forgot her credit card at the store so she ret
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Question 371534: Helen drives from her house to a store at 25 mph. She drives back along the same route at 35 mph. When she gets home she realizes she forgot her credit card at the store so she returns along the same route at 40 mph. When she drives back home along the same route there is a lot of traffic so she travels at 20 mph. What was Helen's average speed for the four trips? Round answer to nearest whole number. Hint: the answer is NOT 30 mph. Answer by amoresroy(361) (Show Source):
You can put this solution on YOUR website! Helen drives from her house to a store at 25 mph. She drives back along the same route at 35 mph. When she gets home she realizes she forgot her credit card at the store so she returns along the same route at 40 mph. When she drives back home along the same route there is a lot of traffic so she travels at 20 mph. What was Helen's average speed for the four trips? Round answer to nearest whole number. Hint: the answer is NOT 30 mph.
Let s = Helen's average speed for the four trips
d = distance from house to store
Average speed = total distance travelled / total time travelled
s = 4*d / [d/25 + d/35 + d/40 + d/20]
note; d cancels outs
s = 4/[1/25 + 1/35 + 1/40 + 1/20]
s = 4/(.14357)
s = 27.86 rounded off to 28
Helen's average speed for the four trips is 28 mph
