For this, the equation is 90× 1.13³=y X was replaced with y. Since she is gaining, you have to remember she is going to have 100 percent of what he had before, she will not lose any. 90× 1.13= 129.86 Now, we need to find the amount of interest she gained, so we have to subtract 90 from the total. 129.86-90=39.86 We can also find the answer by completing a small chart. The first column will be the year. The second will be the amount. The third will be the interest for the year. 1 90 11.7 2 101.7 13.22 3 114.92 14.94 The total would round to 39.86, so her interest for the 3 year would be 39.86, with her having 129.86 altogether.
At the end of each year, the balance is (1 +0.13) times the amount at the beginning of the year. After 3 years, the balance will be .. $90*1.13^3 = $129.86
Of that balance, $90 is the original deposit, so the interest earned is .. $129.86 -90.00 = $39.86
