Focus on each column separately. After the first week, Marcus will have $10 saved. In each consecutive week, the savings will go up by another $10. In the second week, Marcus will have 2* $10, in the third week 3* $10, and so on.
Marcus:
Marcus
Weeks, x
Total Saved ($), y
(x,y)
1
10
(1,10)
2
20
(2,20)
3
30
(3,30)
4
40
(4,40)
David:
David
Weeks, x
Total Saved ($), y
(x,y)
1
15
(1,15)
2
30
(2,30)
3
45
(3,45)
4
60
(4,60)
Practice makes perfect
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* $10 in the second week, 3* $10 in the third, and so on. Notice that the ratio of the savings and the week will always be the same. Let's fill in the second column.
Marcus
Weeks, x
Total Saved ($), y
(x,y)
1
10
2
2*10=20
3
3*10=30
4
4*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* $15 in the second week, 3* $15 in the third, and so on. Let's fill in the second column.
David
Weeks, x
Total Saved ($), y
(x,y)
1
15
2
2*15=30
3
3*15=45
4
4*15=60
Finally, we want to list the results as ordered pairs (weeks,total dollars saved). Let's complete our table.
