Q: One car moving on a straight road covers one third of the distance with 20 km/h and the rest with 60 km/h. the average speed is

(a) 40 km/h

(b) 80 km/h

(c) $46 \frac{2}{3} km/h$

(d) 36 km/h

Ans: (d)

Sol: Average Speed $\large v_{avg} = \frac{s_1 + s_2}{s_1/v_1 + s_2/v_2}$

$\Large = \frac{\frac{1}{3} s + \frac{2}{3}s}{\frac{s}{3v_1}+ \frac{2s}{3v_2}}$