Question
Two trains C and D started from point A and B
respectively. Speed of train D is 21 km/hr more than that of train C. Total distance between point A and B is 495 km. If both the trains meet in 3 hours 40 minutes, then find the speed of train D (in km/hr).Solution
Let the speed of train C be ‘x’ km/hr. Then, speed of train D = (x + 21) km/hr Time = 3 hours 40 minutes = 3(40/60) = 3(2/3) = 11/3 hrs  According to the question, => Speed = Distance/ Time => (x + x + 21) = 495/(11/3) => 2x + 21 = 45 × 3 => 2x = 135 - 21 => x = 57 Speed of train C = x = 57 km/hr Speed of train D = (x + 21) = 78 km/hr
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