SOLUTION: Due Nov. 16 Helen drives from her house to the store at 25 miles per hour (mph). She drives back to her house along the same route at 35 mph. When she gets home, she realiz

Question 369388: Due Nov. 16

Helen drives from her house to the store at 25 miles per hour (mph). She drives back to her house along the same route at 35 mph. When she gets home, she realizes she left her credit card at the store; so she returns (along the same route) at 40 mph. When she drives back to her house (along the same route) there is a lot of traffic so she only travels at 20 mph. What was Helen's average speed for the four trips. Round your answer to the nearest whole number. (Hint: The answer is NOT 30 mph.)

Answer by user_dude2008(1862) (Show Source): You can put this solution on YOUR website!
d=rt
d=25t ----> t = d/25
d=35t ----> t = d/35
d=40t ----> t = d/40
d=20t ----> t = d/20

average speed = total distance/total time = 4d/(d/25+d/35+d/40+d/20) = 5600/201 = 27.8606 mph

Answer: 28 mph
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