Mary's current income y years after starting the job At her current job, Mary gets a $1.5$% raise twice per year. What is
  Mary's current income y years after starting the job at starting
  salary of s, in terms of s and y?


My answer is = s $(1.0075)$^2y. However, correct answer is = s$(1.015)$^2y, Why shouldn't I divide the rate by $2$, as it is being compounded twice per year?
Every time Mary gets a $1.5\%$ raise, her salaray is multiplied by $1.015$. After $y$ years, how many times has she got a raise? $2y$ times. Hence:
$$\text{new salary}=\text{old salaray}\cdot1.015^{2y}$$
The rate of interest is $~1.5\%~$ So according to compound interest formula, we can write it as $~(1 + 1.5/100)~$  which will be $~(1 + 0.015) = 1.015~$ and the time is $~6~$  months so yearly twice So we can write $~Y = 2Y~$.

So the final answer will be $~(1.015)^2~y~$.