We are told that two friends are each saving money in their bank accounts. Marcus saves $$ 10$ each week and David saves $$ 15$ dollars a week. In this exercise, we want to make a table for each friend showing the total amount saved for $1,$ $2,$ $3,$ or $4$ weeks. Then we will list the information as ordered pairs. Let's consider the friends one at a time.

Marcus's Savings

First, let's consider the table that we need to fill in.

Marcus
Weeks, $x$	Total Saved $($),$ $y$	$(x, y)$
$1$
$2$
$3$
$4$

Let's start with the Total Saved column. We know that Marcus saves $$ 10$ a week, so he will have $$ 10$ saved after the first week. In each week after that, his savings will go up by another $$ 10 .$ In other words, Marcus will have $2 \times $ 10$ in the second week, $3 \times $ 10$ in the third, and so on. Notice that the ratio of the savings and the week will always be the same. Let's fill in the second column.

Marcus
Weeks, $x$	Total Saved $($),$ $y$	$(x, y)$
$1$	$10$
$2$	$2 \times 10 = 20$
$3$	$3 \times 10 = 30$
$4$	$4 \times 10 = 40$

Finally, in the last column we want to list the results as ordered pairs $(weeks, total dollars saved) .$ An ordered pair consists of an $x -$ coordinate and a $y -$ coordinate. In our case, weeks represent $x$ and total dollars saved represent $y .$ Knowing this, we can complete our table.

Marcus
Weeks, $x$	Total Saved $($),$ $y$	$(x, y)$
$1$	$10$	$(1, 10)$
$2$	$20$	$(2, 20)$
$3$	$30$	$(3, 30)$
$4$	$40$	$(4, 40)$

David's Savings

Now let's turn to David's table.

David
Weeks, $x$	Total Saved $($),$ $y$	$(x, y)$
$1$
$2$
$3$
$4$

We will start with the Total Saved column again. We know that David saves $$ 15$ a week, so he will have $$ 15$ after the first week. He will add another $$ 15$ to his savings every week after that, meaning that David will have $2 \times $ 15$ in the second week, $3 \times $ 15$ in the third, and so on. Let's fill in the second column.

David
Weeks, $x$	Total Saved $($),$ $y$	$(x, y)$
$1$	$15$
$2$	$2 \times 15 = 30$
$3$	$3 \times 15 = 45$
$4$	$4 \times 15 = 60$

Finally, we want to list the results as ordered pairs $(weeks, total dollars saved) .$ Let's complete our table.

David
Weeks, $x$	Total Saved $($),$ $y$	$(x, y)$
$1$	$15$	$(1, 15)$
$2$	$30$	$(2, 30)$
$3$	$45$	$(3, 45)$
$4$	$60$	$(4, 60)$

Exercise