Question
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 ?
Answer: Option A
Answer: (a)Durga's average speed= $({2xy}/{x + y})$ kmph.= $({2 × 5 × 15}/{5 + 15})$ kmph.= $({2 × 5 × 15}/20)$ kmph = $15/2$ kmphDistance of School = 5 km.Smriti's speed = $15/4$ kmph∴ Required time = $2(5/{15/4})$ hours= $({2 × 5 × 4}/15) = 8/3$ hours= $(8/3 × 60)$ minutes = 160 minutes
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Answer: (a)Durga's average speed= $({2xy}/{x + y})$ kmph.= $({2 × 5 × 15}/{5 + 15})$ kmph.= $({2 × 5 × 15}/20)$ kmph = $15/2$ kmphDistance of School = 5 km.Smriti's speed = $15/4$ kmph∴ Required time = $2(5/{15/4})$ hours= $({2 × 5 × 4}/15) = 8/3$ hours= $(8/3 × 60)$ minutes = 160 minutes
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