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Re: If Mary and Sue enter a 750 meter swimming competition in which Mary g
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11 Jul 2019, 22:43
distance (d) = 700
Sue had 2 mins of head start, it means, by the time Mary started, Sue would have completed a distance of = 2mins x Speed of Sue.
We need to find out whether Mary over takes Sue in this race ?
1) Speed of Mary > 1.5 meters per second (mts), not sufficient, because we don't know the speed of Sue
2) Speed of Sue < 1.3 meters per second (mts), not sufficient, because we don't know the speed of Mary
(1) & (2) --> when Mary is about to start, Sue would have already completed a distance of 2 mins x speed of Sue --> 2x60 (sec)x(<1.3) = (<156 meters), so if Sue continues at a constant rate less than 1.3 mts from this point and Mary continues at a constant rate >1.5 mts, they will meet only around 13 mins after --> 1.5t = 156+1.3t --> t = 13 mins, however, by this time, the race would have completed because race distance is only 700 meters. No, Mary would not over take Sue.
if Mary's speed is 2.0 mts and Sue's is 1.0 mts, then they would meet after 2 mins --> 2.0t = 120 (=1.0x 2minutes - head start) + 1.0t --> t = 2 mins. By this time, both are still within the race distance (700). Yes, Mary would over take Sue.
So, answer is E