Question 103

Durga walks 5 km from her home to school in 60 minutes, then bicycles back to home along the same route at 15 km per hour. Her sister Smriti makes the same round trip, but does so at half of Durga’s average speed. How much time does Smriti spend on her round trip ?

Solution

Durga's walking speed = 5km/hr and bicycle speed = 15 km/hr

=> Average speed = $$\frac{2xy}{x+y}$$ km/hr

= $$\frac{2\times5\times15}{5+15}=7.5$$ km/hr

=> Smriti's speed = $$\frac{7.5}{2}=3.75$$ km/hr

Distance between home and school = 5 km

$$\therefore$$ Time taken by Smriti on the round trip = $$2\times\frac{5}{3.75}=\frac{8}{3}$$ hours

= $$(\frac{8}{3}\times60)=160$$ minutes

=> Ans - (C)

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