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Question

If a train travelled 5 km/hr faster, it would take one hour less to travel 210 km. The speed of the train is :

A
30 km/hr
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B
35 km/hr
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C
70 km/hr
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D
60 km/hr
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Solution

The correct option is A 30 km/hr
Let the speed of the train be x km/hr.
Distance travelled = 210 km

Time taken to travel 210 km = 210x hours

When the speed is increased by 5 km/h, the new speed is (x+5)

Time taken to travel 210 km with the new speed is 210x+5 hours

According to the question,
210x210x+5=1
210(x+5)210x=x(x+5)
210x+1050210x=x2+5x
x2+5x1050=0
(x+35)(x30)=0
x=35,30

The speed cannot be negative. Thus, the speed of the train is 30 km/hr

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