We can model each savings account balance in function of time as a linear function.
Andre starts with $100 and he adds $5 per week. If t is the number of weeks, we can write this as:
[tex]A(t)=100+5\cdot t[/tex]In the same way, as Elena starts with $10 and saves $20 each week, we can write her balance as:
[tex]E(t)=10+20\cdot t[/tex]We can evaluate their savings after 4 weeks (t=4) as:
[tex]\begin{gathered} A(4)=100+5\cdot4=100+20=120 \\ E(4)=10+20\cdot4=10+80=90 \end{gathered}[/tex]After 4 weeks, Andre will have $120 and Elena will have $90.
We can calculate at which week their savings will be the same by writing A(t)=E(t) and calculating for t:
[tex]\begin{gathered} A(t)=E(t) \\ 100+5t=10+20t \\ 5t-20t=10-100 \\ -15t=-90 \\ t=\frac{-90}{-15} \\ t=6 \end{gathered}[/tex]In 6 weeks, their savings will be the same. We know it beca
