Question

Robin is saving money to buy a 720$ phone. she has 105$ saved, and each week she adds 30$ to her savings. write an equation to find the number of weeks (w) until she has enough savings to buy the phone.

Answer 1

Let call w the number of weeks she has been saving.

Then, we can write the expression for her saving in function of the number of weeks as:

`S(w)=105+30\cdot w`

We now have to find the number of weeks it will take for her savings to reach $720.

We can find it by calculating w for S(w)=720:

`\begin{gathered} S(w)-105+30w=720 \\ 105+30w=720 \\ 30w=720-105 \\ 30w=615 \\ w=(615)/(30) \\ w=20.5\approx21 \end{gathered}`

Answer: it will take her 21 weeks to have enough savings.