A person takes 40 minutes more than his usual time when he covers a distance of 20 km at 5 km/h.If he covers the same distance at 8 km/h, he takes x minutes less than the usual time. Whatis the value of x ?

Given that Distance = 20 km ,speed = 5 km/hr

Usual time = $$ \dfrac {20}{5} =  4 hr $$ 

$$ \Rightarrow 4 - \dfrac {40}{60} = 4 - \dfrac {2}{3}$$(according to question)

$$\Rightarrow \dfrac {10}{3} $$

when speed 8 km/hr 

usual time = $$ \dfrac {20}{8} =\dfrac {5}{2}$$

Less than usual time$$   x  = \dfrac {10}{3} - \dfrac{5}{2}$$

$$\Rightarrow \dfrac{5}{6}hr $$

$$\Rightarrow \dfrac {5}{6}\times 60 $$ (change into minute)

$$\Rightarrow 50   min $$ Ans