Question

At the end of the summer, Caitlin had saved $120 from her summer job. This was her initial deposit into a new savings account at the bank. As the school year starts, Caitlin is going to deposit another $5 each week from her allowance. Is her account balance proportional to the number of weeks of deposits? Use the table below. (I would show you one, but I don't know how) Explain your reasoning.

Answer 1

Let x = represent the number of weeks of deposits
A = 120 + 5x the account balance after x weeks
The account balance is directly proportional to the number of weeks of deposits if:
A/x = constant
(120 + 5x)/x = 120/x + 5 is not a constant
For example:
After 1 week there will be: 120 + 1*5 = $125 on the account
After 2 week there will be: 120 + 2*5 = $130 on the account
After 3 week there will be: 120 + 3*5 = $135 on the account
But 125/1 <> 130/2 <> 135/3
The account balance is not proportional to the number of weeks of deposits.