SOLUTION: You and a friend take turns driving on a 450 mile trip. Your friend drives for 3.5 hours at an average speed of 60 miles per hour. What must your average speed be for the remainder

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Question 892020: You and a friend take turns driving on a 450 mile trip. Your friend drives for 3.5 hours at an average speed of 60 miles per hour. What must your average speed be for the remainder of the trip if you want to reach your hotel in 4 more hours.
My work:
60 x 3.5(the hours te friend drove) = 210
4/210 = 52.5
52.5 miles/hour
However my brother checked it and told me it was wrong and I'm not sure what I did.

Found 3 solutions by Alan3354, josgarithmetic, richwmiller:
Answer by Alan3354(69443)   (Show Source):
You can put this solution on YOUR website!
You and a friend take turns driving on a 450 mile trip. Your friend drives for 3.5 hours at an average speed of 60 miles per hour. What must your average speed be for the remainder of the trip if you want to reach your hotel in 4 more hours.
My work:
60 x 3.5(the hours te friend drove) = 210
This much is correct, your friend drove 210 miles.
That leaves 240 miles to go (450 - 210)
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To go 240 miles in 4 hours:
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d = r*t
r = d/t = 240/4
=======================================
4/210 = 52.5
4/210 is not 52.5
4/210 =~ 0.019, a meaningless number for this problem.
52.5 miles/hour
---
Include the units in your calculations.
4 hr/210 miles = 0.019 hours/mile ???? No one wants to know that.
However my brother checked it and told me it was wrong and I'm not sure what I did.

Answer by josgarithmetic(39617)   (Show Source):
You can put this solution on YOUR website!
__________________rate_______time_______distance
YOU________________r_________4__________r*4
FRIEND____________60_________3.5________210
Total___________________________________450

Answer by richwmiller(17219)   (Show Source):
You can put this solution on YOUR website!
60 x 3.5= 210
Your friend drove 210 miles
the total trip is 450
450-210=240
You need to drive 240 more miles.
240/4=60 mph
You must continue to average 60 mph. to complete the remaining part in 4 hours