Question

a car completes a journey at an average speed of 40 km/h .At what speed must it travel on the return journey if the average speed for the complete journey (out and back)is 60 km/h

Answer 1

Answer:

Let the distance one way be S km

Let the speed for return journey be x km/ hour

Total Distance = S + S = 2S

Total Time taken = S / 40 + S / x = S ( x+40) /40x

Average speed = Total Distance / Total Time = 2S / S(x+40)/40x = 60

2*40x / ( x+40) = 60

40x = 30x + 1200

10x = 1200

x = 120 mph ANSWER

CHECK

S/40 + S /120 = 4S/120= S /30

2S / S /30 = 60 mph

Step-by-step explanation:

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