Alex and Brian run a marathon. Alex starts first and Brian starts 7 hours after Alex at twice the speed of Alex. Brian takes an hour of rest every $2^{n d}$ hour for an hour. After how long does Brian reach to Alex?

21 hours

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28 hours

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14 hours

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35 hours

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Solution

The correct option is B 28 hours
Let us say, 1 unit distance is traveled by Alex in 1 hour. Therefore, 2 units of distance is traveled by Brian in 1 hour.

At 7 hours, Brian is at 0 distance from his starting.
Alex is 7 units at this point.

Brian travels for 2 hours and rests for 1 hour; so, he covers 4 units in 3 hours.

In the same time, Alex covers 3 units.
So, every 3 hours, Brian comes 1 unit closer to Alex.

Time taken to cover 7 units = 21 hours
Since Brian started 7 hours late, total time = 28 hours

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Alex and Brian run a marathon. Alex starts first and Brian starts 7 hours after Alex at twice the speed of Alex. Brian takes an hour of rest every 2nd hour for an hour. After how long does Brian reach to Alex?

Alex and Brian run a marathon. Alex starts first and Brian starts 7 hours after Alex at twice the speed of Alex. Brian takes an hour of rest every $2^{n d}$ hour for an hour. After how long does Brian reach to Alex?