The correct answer is A. Rs 30.00.
The expected capital gain is the difference between the expected final price and the original investment. In this case, the expected capital gain is Rs 20, and the expected final price is Rs 50. Therefore, the original investment must be Rs 30.
Option B is incorrect because the expected capital gain is positive, so the original investment cannot be negative.
Option C is incorrect because the expected final price is Rs 50, so the original investment cannot be Rs 70.
Option D is incorrect because the expected capital gain is positive, so the original investment cannot be negative.