Question

Nikhil while driving to office , computer the average speed for his trip to be 20km/h .on his Rerun trip along the Sam route , the average speed is 30km/h . What is the average speed of his trip

Answer 1

distance = speed * time
For going trip:
distance = s , time = t1
s = 20 * t1
t1 = s/20
For return trip:
distance = s (distance is same), time = t2
s = 30 * t2
t2 = s/30
Average speed = total distance/total time
$average \: speed = \frac{s + s}{ t1 + t2 } \\ = \frac{2s}{ \frac{s}{20} + \frac{s}{30} } = \frac{2s}{ \frac{3s + 2s}{60} } \\ = 2s \times \frac{60}{5s} = 24 \: \frac{km}{h}$
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