SOLUTION: If you drove for 30 minutes at 60 mph and 10 minutes at 38 mph. What was your average speed for the trip?

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Question 711756: If you drove for 30 minutes at 60 mph and 10 minutes at 38 mph. What was your average speed for the trip?
Found 2 solutions by checkley79, Edwin McCravy:
Answer by checkley79(3341) About Me  (Show Source):
You can put this solution on YOUR website!
D=RT
D=60*.5
D=38*.167
D=60*5+38*.167
D=30+6.346
D=36.346 MILES.
36.346=R(.5+.167)
36.346=.667R
R=36.346/.667
R=54.34 MPH. IS THE AVERAGE SPEED.

Answer by Edwin McCravy(20064) About Me  (Show Source):
You can put this solution on YOUR website!
The other tutor used decimals and rounded off, making his answer off
a little.  I'll use fractions.

We use two formulas:

Distance = Rate × Time

Average Rate = Total Distance ÷ Total Time

When you went 30 minutes (half an hour) at 60 mph,
you went 60×1%2F2 = 30 miles  

When you went 10 minutes (1%2F6 of an hour) at 38 mph,
you went 38×1%2F6 = 38%2F6 =  19%2F3 = 6%261%2F3 miles 

To find the total distance, we use the improper fraction for
the distance at 38 mph 

Total distance = 30%22%22%2B%22%2219%2F3%22%22=%22%2290%2F3%22%22%2B%22%2219%2F3%22%22=%22%22109%2F3 or 36%261%2F3 miles.

 Total time = 1%2F2%22%22%2B%22%221%2F6%22%22=%22%223%2F6%22%22%2B%22%221%2F6%22%22=%22%224%2F6 or 2%2F3 hr.

Average Rate = Total Distance ÷ Total Time

We will use the improper fraction for the total miles  

Average Rate = 109%2F3÷2%2F3%22%22=%22%22109%2F3%22%22%2A%22%223%2F2%22%22=%22%22109%2Fcross%283%29%22%22%2A%22%22cross%283%29%2F2%22%22=%22%22109%2F2%22%22=%22%2254%261%2F2mph.

Edwin