A) 72
B) 45
C) 54
D) 50
Correct Answer: D
Solution :
[d] Let the length of train be x km and its speed by kmph. \[\therefore \frac{x}{y-\,2}=\frac{9}{3600}=\frac{1}{400}\] ? (i) \[\frac{x}{y-\,4}=\frac{10}{3600}=\frac{1}{360}\] ... (ii) By dividing equation (i) by (ii), \[\frac{y-\,4}{y-\,2}=\frac{360}{400}=\frac{9}{10}\] \[\Rightarrow 10y-\,40=9y-\,18\] \[\Rightarrow y=40-\,18=22\] From equation (i), \[\frac{x}{22-\,2}=\frac{1}{400}\] \[\Rightarrow x=\frac{1}{20}\,\,km=\frac{1000}{20}=50\,\,metre\] Alternate Method: Let Speed of train be x km/h According to question \[(x-2)\,\,\frac{5}{18}\times 9=(x-y)\,\,\frac{5}{18}\times 10\] \[9x-\,18=10x-\,40\] \[x=22\,\,km/h\] \[\operatorname{Re}quired\,\,lenght=(22-\,2)\frac{5}{18}\times 9=50\,\,m\]You need to login to perform this action.
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