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Question

John covered a part of his journey at 20 kmph, and the remaining part at 70 kmph. He took a total of 8 hr to cover a distance of 400 km. For how much time did he travel at 20 kmph?

A
4 hr and 12 min
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B
3 hr and 20 min
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C
4 hr and 40 min
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D
3 hr and 12 min
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Solution

The correct option is A 3 hr and 12 min
Let the total time that John has travelled at the speed of 20 kmph be T.

Distance is the product of speed and time. Hence, the distance covered at a speed of 20 kmph is:
s1=20×T.........(i)

The total time taken covered is 8 hr. Thus, the time to cover the remaining distance is:
t2=8T

The remaining distance which is covered at a speed of 70 kmph is:
s2=70×(8T).......(ii)

Given, the total distance covered:
s=400 km.......(iii)
But,
s=s1+s2
From (i), (ii) and (iii), we get
400=20×T+70×(8T)
50×T=160
T=3.2 hr
We know 1 hr=60 min
0.2 hr=0.2×60=12 min
T=3 hr and 12 min

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