Question

A car is moving on a straight road covers one third of the distance with a speed of 20 km/h and the rest with
a speed of 60 km/h. The average speed of the car is
(1) 40 km/h
(2) 50 km/h
(3)36 km/h
(4) 55 km/h
​

Answer 1

Answer:

36 km I'm not sure about the answer

Answer 2

$\sf \large We\;know\;that,$

$\sf \to One-third\;of\;the\;distance\;is\;covered\;with\;speed\;of\;20\;km/h\;and\;the\;rest\; two-third\;of\;the\;distance\;with\;the\;speed\;of\;60\;km/h.$

$\sf \large So,$

$\sf \to Let\;the\;distance\;travelled\;by\;the\;car\;on\;straight\;path\;be\;x.$

$\sf \large Now,$

$\sf \to Time\;required\;for\;one-third\;of\;the\;journey\;is\;\frac{\frac{x}{3}}{20}=\frac{x}{60}$

$\sf \to Time\;required\;for\;rest\;part\;of\;journey\;is\;\frac{\frac{2x}{3}}{60}=\frac{x}{90}$

$\sf \to Total\;time\;taken\;to\;complete\;the\;journey\;is\;\frac{x}{60}+\frac{x}{90}=\frac{x}{36}$

$\sf \boxed{Average\;speed=\frac{total\;distance\;travelled}{total\;time\;taken}}$

$\sf \to Average\;speed=\frac{x}{\frac{x}{36}}=\frac{36\cancel{x}}{\cancel{x}}$

$\sf \boxed{Average\;speed=36\;km/h}$