Question

Q71f a journey is covered with firsthall distance at speed 120 km/h and Second
half of the distance at a speed of 60 km/h. Find average speed?
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Answer 1

Answer is 90km/h

Explanation:

First half distance at speed 120 km/h

second half distance at speed 60 km/h

average speed = (½X120) + (½X60)

= 60 + 30 = 90km/h

Answer 2

Explanation:

Let the distance be 120 km.

$\sf \: Speed \: at \: firsthalf \: distance \\---------------------------- \\ \longrightarrow = \: \tt\frac{Distance}{time} = \frac{60}{120} = 0.5 \: hr \\ ----------------------------\\ \sf \: Speed \: at \: secondhalf \: distance \\ \longrightarrow \: \tt\frac{60}{60} = 1.5hr \\ ---------------------------- \\ \tt \: Average \: speed = \frac{120}{1 + .5} = \frac{ \cancel{120}}{ \cancel{1.5}} = 80 \: km/hr \\ ----------------------------$