a boy runs for 10 min at a uniform speed of 9 km/h. at what speed should he run for the next 20 min. so that the his speed is comes to 15 km/h?
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Distance covered in 10 minutes = 9 kmph * 10/60 hrs = 1.5 km
Speed for the 2nd leg = V kmph
Distance coveed in 2nd leg = V * 20/60 = V / 3 km
Overall average speed = total distance / total time =
( 1.5 + V/3 ) / (10+20)/60 = 12 km ph
2 (1.5 + V/3) = 12
1.5 + V/3 = 6
V = 13.5 KMPH
Speed for the 2nd leg = V kmph
Distance coveed in 2nd leg = V * 20/60 = V / 3 km
Overall average speed = total distance / total time =
( 1.5 + V/3 ) / (10+20)/60 = 12 km ph
2 (1.5 + V/3) = 12
1.5 + V/3 = 6
V = 13.5 KMPH
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