A 300 m long train crosses a platform in 42 sec while it crosses a signal pole in 18 sec. What is the length of the platform?  Choose the correct choice.
A) 288
B) 350
C) 400
D) 276
E) 234
Speed = 300/18 = 50/3 m/sec.   Let the length of the platform be x meters.   Then, (x + 300)/42 = 50/3   3x + 900 = 2100 =&gt; x = 400 m.   Answer:400
<result>C</result>
A 300 m long train crosses a platform in 42 sec while it crosses a signal pole in 18 sec. What is the length of the platform?