Final answer:
Mary earns R300 in interest in the first three years at 5% p.a., and after adding R7000 and changing the interest rate to 15% p.a., she earns R2790 over the next two years. The total interest Mary earns is R3090, a result that does not match any of the provided answer choices.
Step-by-step explanation:
The question we are addressing is: What is the total interest earned on Mary's investment if she withdraws all the money from the investment 2 years after adding R7000, with an initial interest rate of 5% p.a. for three years, which then changes to 15% p.a.?
First, we need to calculate the interest Mary earns in the first three years on her initial R2000 at 5% per annum. Using the simple interest formula, Interest = Principal × Rate × Time, we get:
Interest = R2000 × 5% × 3
Interest = R2000 × 0.05 × 3 = R300
After three years, Mary adds R7000 to her account, which now has a total of R2000 + R300 + R7000 = R9300. The new interest rate is 15% per annum, which will be in effect for the next 2 years. So the interest for the next 2 years will be:
Interest = R9300 × 15% × 2
Interest = R9300 × 0.15 × 2 = R2790
Total interest earned over 5 years is the sum of interest from both periods:
Total Interest = R300 + R2790 = R3090
However, none of the options provided (a) R7000, (b) R7500, (c) R8000, or (d) R8500, match the correct calculation of R3090. Therefore, there seems to be a discrepancy in the provided answer choices. Mary actually earns a total of R3090 in interest.