Question

Alfredo is buying a watch for $200. He will make an initial payment of $50 and then pay the remaining balance in payments for $15 per week. Which function can be used to find a, the amount he will still need to pay at the end of n weeks? *

Answer 1

The Correct answer is a= -15n+150

Explanation:

At first, you may look for the equation a=15n+50, but this wouldn't work because we're trying to find out how much he will still need to pay, not how much he has paid.

So, let's think about this

When you subtract the initial amount paid (50) from the cost (200) you get 150. Next, we know he pays 15 each week. To find out how much is left to pay, we would normally subtract the amount we've paid from the total. However, adding a negative to a positive is the same as subtracting a positive from a positive. So we can do -15n as a way of finding out how much we've paid off that week. Then, we'd add it to 150 to find out how much left we need to pay

For Example:

Lets say we're 2 weeks in

a=(-15*2)+150=120

We can confirm this is the right answer by doing 200-[50+(15*2)]=120.