Question

during first half of a journey a body travles with a speed of 40 km/hr and in next half it travels with a speed of 20 km/hr calculate the average speed of the whole journey

Answer 1

Let the total distance  be  2x .

in first  half journey,

$distance = x \\ \\ speed = 40 \ km/h \\ \\ time (t_1) = \frac{distance}{speed}  \\ \\ t_1 =  \frac{x}{40}$

in second  halg  journey,

$distance = x \\ \\ speed = 20 \ km/h \\ \\ time (t_2) = \frac{distance}{speed}  \\ \\ t_1 =  \frac{x}{20} \\ \\  \text{We know that, } \\ \\ \text{Average Speed} = \frac{total \ distance}{total \ time}  = \frac{2x}{t_1 + t_2} \\ \\ = \frac{2x}{ \frac{x}{40} + \frac{x}{20} }  \\ \\  = \frac{2}{ \frac{1}{40} + \frac{1}{20} } \\ \\ = \frac{40}{ \frac{1}{2} + 1 } \\ \\ = \frac{80}{3} \  km/h$

Answer 2

Average Speed=26.66km/hr