A,B and C enter into a partnership by investing in the ratio of 5:5:8. After one year A additionally invests Rs. 4900 and B withdraws Rs. 3700. Now, the ratio of investment changes to 5:4:7. What amount did A invest initially? (in Rs.)

Answer is Rs 38,100.
Assume net initial investment was 18x. So, respective investments of A,B, and C would be 5x,5x and 8x. But after one year A's net investment is 5x+4900 and that of B is 5x-3700. As given in the question we find the ratio of investment of A to that of B after one year is 5:4. So, we can simply solve the below equation to get our answer:
(5x+4900):(5x-3700) = 5:4.

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