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

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

RELATED QUESTIONS
Due Nov. 16 Helen drives from her house to the store at 25 miles per hour (mph).... (answered by user_dude2008)

Starting at home, Stephanie traveled uphill to the gift store for 30 minutes at just 10... (answered by Alan3354)

Please help me! Starting at home, Jessica travelled uphill to the hardware store for... (answered by josgarithmetic,MathTherapy,Alan3354)

Starting at home, Emily traveled uphill to the grocery store for 20 minutes at just 6... (answered by josmiceli)

She drives 10 miles from her friend to the motorway 240 miles on the motorway 5 miles to... (answered by ankor@dixie-net.com)

Julie drives 100 mi to her Grandmother's house. On the way to Grandmother's, she drives... (answered by JulietG)

Danielle drives from her home to the store at an average speed of 40 miles per hour. She... (answered by amoresroy)

Elda walked from her home to her friend Niabi's house at 4.5 km/hr. When Elda returned... (answered by Alan3354)

Danielle drives from her home to the store at an average speed of 40mph. She returns... (answered by algebrahouse.com)