A train crosses a post in 15 seconds and a platform 100 m long in 25 seconds. Its length is  Pick one:
A) 75
B) 100
C) 125
D) 175
E) 150
Assume x is the length of the train and v is the speed   x/v = 15 =&gt; v = x/15   (x+100)/v = 25 =&gt; v = (x+100)/25   Ie, x/15 = (x+100)/25   =&gt; 5x = 3x+ 300   =&gt; x = 300/2= 
<gadget id="calculator">300/2</gadget>
<output>150</output>
150   Answer is 150.
<result>E</result>
A train crosses a post in 15 seconds and a platform 100 m long in 25 seconds. Its length is