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Question

It took AndreaAndrea 2.72hours to drive to her mother's house on Wednesday morning. On her return trip on Thursday night, traffic was heavier, so the trip took her 3 hours. Her average speed on Thursday was 7 mph slower than on Wednesday. What was her average speed onThursday?
Andrea 's average speed on Thursday was ?

Answer 1

You need to make use of the Distance formula, which says that Distance = Speed x Time.

 

Obviously the distances going both ways are the same, so you can set the expressions for each distance equal to each other.

 

Let's first find the distances each way.  Let s = speed on Wed

 

d_{1 =} (s)(2.72)

d₁ = 2.72s

 

d₂ = (s-7)(3)
d₂ = 3(s-7)

d₂ = 3s - 21

 

Now you can set d₁ and d₂ equal to each other

 

2.72s = 3s - 21

 

You can solve to get s, which is the Wed speed, from which you can get the Thurs speed.

 

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