Answer: $120
First, create a function
- x = number of week
- y = amount of money in savings
- a = amount of money added each week
- b = the amount of money in savings at week 0
[tex]\left \{ {{5a+b=45} \atop {12a+b=80}} \right.\\\\(5-12)a+(1-1)b=45-80\\\\-7a=-35\\\\a=\frac{-35}{-7} =5\\\\5a+b=45\\\\5(5)+b=45\\\\b=45-25=20[/tex]
Therefore, the function is y = 5x + 20
To find the amount of money at week 20, set x = 20 and solve:
[tex]y=5(20)+20=100+20=120[/tex]
Therefore, the answer is $120.
