
Muzammil H. answered 02/18/15
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Enthusiastic Biomedical Engineer ready to help in STEM.
Good job on determining $17,200, however that is not the total interest, that is the interest + her original investment.
Her original investment totals $16,000, and her interest paid is $1,200 (0.03 * 7,000 = 210, 0.11*9,000 = 990, 210 + 990 = 1,200). This gives you that total of $17,200.
Now, a percentage is defined as a part over a whole. The "part" is the interest paid ($1,200) and the whole is the new value of her investment, the $17,200. Doing 1,200/17,000 gives you 0.070588, or 7.0588% interest for the total investment.