Question

A boy runs for 20 min. at a uniform speed of 18km/h. At what speed should he run for the next 40 min. so that the average speed comes 24km/hr.

Answer 1

A boy means X and 20 minutes per hour at a uniform speed of 18km.h. so that the average speed comes is next 40 minutes. ok that answer was 20 km per hour seems like

Answer 2

"The speed the boy runs for next 40 minutes is $27{ \quad Km }/{ hr }$

Solution:

We know that,

$Average\quad speed\quad =\quad \frac { Total\quad distance }{ Total\quad timetaken }$

Let us consider if a boy runs 18Km in 20min and in 40 min he runs x speed

Total distance = 18 Km in 20min (to convert in hour. so divided by 60) + x Km in 40min (divide by 60)

Total minutes = 20 + 40 = 60

$Speed\quad =\quad 24{ \quad Km }/{ hr }$

Therefore, By applying the values we get

$24=18\times (\frac { 20 }{ 60 } )+x(\frac { 40 }{ 60 } )Km/(20+40)$

By simplifying we get,

$24=6+(\frac { 2 }{ 3 } )x$

$18=(\frac { 2 }{ 3 } ) x$

${ x }=27{ \quad Km }/{ hr }$"