Two boys started running. A runs 10 kmph and B runs 7 kmph.If they start from the same place in opposite directions, in what time will they be 102 km apart?

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Solution

suppose that they will start from ponit A
given that they runs in opposite direction
a have 10 kmph
b have 7 kmph
think about after one hour
a will be 10 km away from point A since has speed is 10 kmph
b will be 7 km apart from point A
now we can see that they are 10+7 =17 km away from each other
for next one hour they will be separated from another 17 km and so on
and time for 102 km distance =102/17= 6 hours
*alternately
they are travelling in opposite direction so net velocity= 17 kmph
Velocity= distance / time
we have distance =102 km
velocity = 17 kmph
so time = 102/17= 6 hours

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