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Question

From 09:00 pm to 10:00 pm, a person drove at a speed of 40 km/h, then he took a halt for an hour. He resumed his journey at 11:00 pm and drove till 12:00 am midnight at a speed of 50 km/h. What is his average speed in the time interval between 09:00 pm and 12:00 am?

A
90 km/h
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B
40 km/h
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C
30 km/h
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D
45 km/h
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Solution

The correct option is C 30 km/h
We know that,
Speed = Distancetime
Distance = Speed × time

Between 9:00 pm and 10:00 pm,
Distance travelled = 40 km/h × 1 h
= 40 km

Between 10:00 pm and 11:00 pm, the person doesn’t travel.
So, the distance travelled = 0

Between 11:00 pm and 12:00 am,
Distance travelled = 50 km/h × 1 h
= 50 km

For the whole journey,
Average speed = Total distanceTotal time
= (40 +0+ 50) km(1 + 1 + 1) h= 903km/h = 30 km/h

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