Question 132

A boat, while going down-stream in a river covered a distance of 50 miles at an average speed of 60 miles per hour. While returning, because of the water resistance, it took one hour fifteen minutes to cover the same distance. What was the average speed during the whole journey?

Solution

Time taken by boat to go downstream = $$\frac{50}{60}=\frac{5}{6}$$ hours

Time taken for upstream distance = $$1+\frac{1}{4}=\frac{5}{4}$$ hours

Total time = $$\frac{5}{6}+\frac{5}{4}=\frac{25}{12}$$ hours and total distance covered = $$50+50=100$$ miles

$$\therefore$$ Average speed = total distance/total time

= $$\frac{100}{\frac{25}{12}}=48$$ mph

=> Ans - (B)

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