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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.

Respuesta :

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:

[tex]S(w)=105+30\cdot w[/tex]

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:

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

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

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