kevin invests money in an account paying simple interest. he invests $40 and no money is added or removed…

Explanation:

Step1: Recall simple interest formula

The formula for simple interest is $A = P(1 + rt)$, where $A$ is the amount after time $t$, $P$ is the principal amount, $r$ is the annual interest rate (in decimal), and $t$ is the time in years. Here, $P = 40$, $A = 42.80$, and $t = 1$ (since it's one year).

Step2: Substitute values into the formula

Substitute the known values into the formula: $42.80 = 40(1 + r\times1)$.

Step3: Solve for r

First, divide both sides by 40: $\frac{42.80}{40}=1 + r$. Calculate $\frac{42.80}{40}=1.07$. So, $1.07 = 1 + r$. Then subtract 1 from both sides: $r = 1.07 - 1 = 0.07$. To convert this to a percentage, multiply by 100: $r = 0.07\times100 = 7%$.

Answer:

The simple interest rate per year is 7%.