High School

Each month, Barry makes three transactions in his checking account:

- He deposits [tex] \$700 [/tex] from his paycheck.
- He withdraws [tex] \$150 [/tex] to buy gas for his car.
- He withdraws [tex] \$400 [/tex] for other expenses.

If his account balance is [tex] \$1,900 [/tex] at the end of the 1st month, which recursive equation models Barry's account balance at the end of month [tex] n [/tex]?

A. [tex] f(1) = 1,900 [/tex]
[tex] f(n) = f(n-1) - 150 [/tex], for [tex] n \geq 2 [/tex]

B. [tex] f(1) = 1,900 [/tex]
[tex] f(n) = 150 \cdot f(n-1) [/tex], for [tex] n \geq 2 [/tex]

C. [tex] f(1) = 1,900 [/tex]
[tex] f(n) = f(n-1) + 150 [/tex], for [tex] n \geq 2 [/tex]

D. [tex] f(1) = 1,900 [/tex]
[tex] f(n) = f(n-1) + 700 [/tex], for [tex] n \geq 2 [/tex]

Answer :

To solve this problem, let's break down Barry's transactions and see how they affect his account balance each month.

Each month, Barry:
1. Deposits [tex]$700 into his account.
2. Withdraws $[/tex]150 for gas.
3. Withdraws [tex]$400 for other expenses.

To find the net change in his account balance each month, we can calculate it by looking at the total deposits and withdrawals:

- Total deposits = $[/tex]700
- Total withdrawals = [tex]$150 (gas) + $[/tex]400 (expenses) = [tex]$550

The net change in the balance each month is therefore:
\[ \text{Net change} = 700 - 550 = 150 \]

Barry's account balance at the end of the first month is $[/tex]1,900. From the second month onward, the balance changes by [tex]$150 each month. We can express this situation as a recursive equation:

1. The initial condition is that at the end of the first month, his balance is $[/tex]1,900:
[tex]\[ f(1) = 1,900 \][/tex]

2. For any month [tex]\( n \geq 2 \)[/tex], the account balance is the previous month's balance plus the net change of [tex]$150:
\[ f(n) = f(n-1) + 150 \]

Therefore, the recursive equation that models Barry's account balance at the end of month \( n \) is:

C. \( f(1) = 1,900 \)
\( f(n) = f(n-1) + 150 \), for \( n \geq 2 \)

This equation accounts for the monthly deposit and withdrawals, reflecting the net increase of $[/tex]150 each month.