It took Brian 12 hours to drive to a football game. On the way home, he was able to increase his average speed by 15mph and make the return drive in only 9 hours. Find his average speed on the return drive.
Answers
Let the distance be X miles.
Average speed to drive to football game = X/12 mph
Now on the way back his average speed increases by 15mph, so his average speed is (X/12 + 15) mph. Time taken is 9 hours.
So, (X/12 +15) = X/9
On solving this equation X comes out to be 540 miles.
Average speed on the return drive is 60mph.
Given :- It took Brian 12 hours to drive to a football game. On the way home, he was able to increase his average speed by 15mph and make the return drive in only 9 hours. Find his average speed on the return drive. ?
Solution :-
Let us assume that, Original speed of Brain while going for Job interview was x km/h .
so,
→ speed * Time = Distance
→ x * 12 = 12x km .
now,
→ New speed = (x + 15) km/h .
→ Time = 9 hours.
then,
→ Distance = 9(x + 15) km.
since, both distance is same ,
→ 9(x + 15) = 12x
→ 9x + 135 = 12x
→ 12x - 9x = 135
→ 3x = 135
→ x = 45 km/h .
a
therefore,
→ Speed while return drive = 45 + 15 = 60 km/h . (Ans.)
Hence, Brian average speed on the return drive is 60km/h .
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