SOLUTION: May you please help me with this question? The distance from Calgary to red deer is approximately 140 km. Some friends leave Calgary at noon, drive to red deer, have a half-hour

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Question 1011507: May you please help me with this question?
The distance from Calgary to red deer is approximately 140 km. Some friends leave Calgary at noon, drive to red deer, have a half-hour break, and then return to Calgary. They arrive at 3:15 p.m. Traffic is busier on the return trip, so their average speed is 10km/h slower than on the outbound trip. What is the average speed of the round trip?
*hint* the textbook answer is 107 km/h
Steps/Calculations please?
Found 2 solutions by josgarithmetic, MathTherapy:
Answer by josgarithmetic(39630) About Me  (Show Source):
You can put this solution on YOUR website!
            speed       time            distance

GOING         r         3%261%2F4-1%2F2        140

RETURN      r-10        ()               140

Total                   (?)              280


Using RT=D basic travel rate rule, r can be found and applied to fill the other cells.
r=140%2F%283%261%2F4-1%2F2%29 
            speed             time            distance

GOING         560%2F11       2%263%2F4        140

RETURN      450%2F11         %28154%2F11%29       140

Total                         165%2F11          280


Average distance accounting only for time traveling,
280%2F%28165%2F11%29
280%2F15=56%2F3
highlight%2818%262%2F3%29---average speed for traveling time only



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Be aware, I did not check this for mistakes.

Answer by MathTherapy(10557) About Me  (Show Source):
You can put this solution on YOUR website!

May you please help me with this question?
The distance from Calgary to red deer is approximately 140 km. Some friends leave Calgary at noon, drive to red deer, have a half-hour break, and then return to Calgary. They arrive at 3:15 p.m. Traffic is busier on the return trip, so their average speed is 10km/h slower than on the outbound trip. What is the average speed of the round trip?
*hint* the textbook answer is 107 km/h
Steps/Calculations please? 
Difference in speeds is irrelevant

Total distance: 2(140), or 280 km

Total time: 2%263%2F4 (3%261%2F4+-+1%2F2) hours 

Average speed: Total_distance%2FTotal_time -------> 280%2F%282%263%2F4%29

This doesn't result in an AS of 107 km/h. You need to check why!