A man has to cover a distance of 387 km in 21 hours. If he covers two – third of this distance in $$\frac{5}{7}$$ of the time, then what should his speed (in km/hr) be to cover the remaining distance in the time left?

Correct option is A

Given:

Total distance D = 387 km

Total time T = 21 h

Covered $$\frac{2}{3}$$​ of distance in $$\frac{5}{7}$$​ of the time

Find: Required speed to cover the remaining distance in the remaining time

Formula Used:

Speed = $$\dfrac{\text{ distance}}{\text{ time}}$$​​

Solution:
Covered distance = $$\frac{2}{3} \times 387$$​= 258 km
Time used = $$\frac{5}{7} \times 21 = 15$$​ h

Remaining distance = 387 - 258 = 129 km
Remaining time = 21 - 15 = 6 h

Required speed = $$\dfrac{129}{6} =$$​ 21.5 km/h