A) 40.8
B) 51
C) 30.6
D) 61.2
Correct Answer: A
Solution :
Let the speed of Rajdhani be\[x\]kmph, and the speed of express train be\[y\]kmph. According to the question, \[\frac{612}{y}-\frac{612}{x}=9\] ? (i) and, \[\frac{612}{x}-\frac{612}{2y}=3\] ? (ii) By equation (i) \[\times \frac{1}{2}+\](ii), \[\frac{612}{2y}-\frac{612}{2x}+\frac{612}{x}-\frac{612}{2y}\] \[=\frac{9}{2}+3\] \[\Rightarrow \frac{612}{x}-\frac{612}{2x}=\frac{15}{2}\] \[\Rightarrow \frac{612}{2x}=\frac{15}{2}\Rightarrow \frac{306}{x}=\frac{15}{2}\] \[\Rightarrow x=\frac{306\times 2}{15}=40.8\,kmph\]
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