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Max@Math Revolution wrote:
[GMAT math practice question]

John traveled the entire 50 km trip. If he travelled the first 20 km of the trip at a constant rate 40 km per hour and the remaining trip at a constant rate 20 km per hour, what is his average speed, in km per hour?

A. 20 km/h
B. 23 km/h
C. 25 km/h
D. 26 km/h
E. 27 km/h
Average speed = total distance/total travel time

total distance = 50 km

total travel time = time spent driving at 40 kmh + time spent driving at 20 kmh
time = distance/speed
So, time spent driving at 40 kmh = 20/40 = 1/2 hour
And time spent driving at 20 kmh = 30/20 = 3/2 hours
So, TOTAL travel time = 1/2 + 3/2 = 4/2 = 2 hours

Average speed = 50/2 = 25 kmh

Cheers,
Brent

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Max@Math Revolution wrote:
[GMAT math practice question]

John traveled the entire 50 km trip. If he travelled the first 20 km of the trip at a constant rate 40 km per hour and the remaining trip at a constant rate 20 km per hour, what is his average speed, in km per hour?

A. 20 km/h
B. 23 km/h
C. 25 km/h
D. 26 km/h
E. 27 km/h
Leg 1:
T = D/S
T = 20/40 = 1/2

Leg 2:
T = D/S
T = 30/20 = 3/2

Total time = 1/2 + 3/2 = 2

Avg Speed = D/T = 50/2 = 25

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Ave Speed = ( Total Distance ) / ( Total Time )
The total distance = 50 km.
Total time is 20 / 40 + 30 / 20 = 0.5 + 1.5 = 2
The average speed is 50 / 2 = 25.

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