Question
Two trains, A and B, cross each other in 15 seconds and
35 seconds respectively, when running in opposite and the same direction respectively. If the speed of the slower trains is n% of the speed of the faster trains, then find the value of (n × 2).Solution
Let the speed of train A be S1 and the speed of train B be S2. And length of train A be L1 and the length of train B be L2. According to the question, (S1 + S2) = (L1 + LB)/15 And, (S1 - S2) = (L1 + LB)/35 Here, the length of both the train is equal. So, (S1 + S2) × 15 = (S1 - S2) × 35 => 15 S1 + 15 S2 = 35 S1 – 35 S2 => 20 S1 = 50 S2 => S1/S2 = 50/20 = 5/2 Speed of slower train = n% of faster train => n% = (2/5) × 100 = 40% Therefore, (n × 2) = 40 × 2 = 80
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