Question

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

Answer 1

car covers the one third of the distance with speed=20km/hr
Distance=?
time taken=?

$speed = \frac{ distance}{ time}$
$20 = \frac{d}{t}$
By cross multiply,
$t = \frac{d}{20}$
Rest covers with speed of= 60km/hr

Same formula,
$s = \frac{d}{s}$

$60 = \frac{d}{t}$

By cross multiply,
$t = \frac{d}{60}$
$total \: distane = d + d = 2d \\ tota \: time = \frac{d}{20} + \frac{d}{60 } = \frac{4d}{60}$

Aeverage speed
$\frac{2d}{\frac{4d}{60} }$
$2d \times \frac{60}{4d}$
aeverage speed=30km/hr