How to solve this Ratio problem

I am preparing for an olympiad and came across the following question in a workbook. There is answer but no explanation:

The ratio between the number of passengers travelling by Ist and IInd class between two railway stations is 1:50, whereas the ratio of Ist and IInd class fares between the same stations is 3:1.If on a particular day, Rs. 1325 is collected from the passengers travelling between these stations by these classes, then what was the amount collected from the IInd class passengers?

(A)Rs.750 (B)Rs.850 (C)Rs.1000 (D)Rs.1250

I want to know the explanation to the answer.

Note:Rs. stands for INR(Indian Rupee) which is the currency of India

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Sorry for the tag, I saw no other suitable tag for this question – Govind Balaji Oct 2 '13 at 7:23

I think D is the correct answer. Suppose in a day $x$ number of passengers travel by 1st class, then $50x$ number of passengers will travel by 2nd class. Now if each passenger in 1st class pays Rs. $3y$, then each of 2nd class will pay Rs. $y$. Now by hypothesis, $3xy+50xy=1325$. Thus $50xy=1250$.