How to Solve Problems with a Cartesian Graph

You can use a Cartesian graph to solve certain types of math problems. When you draw two lines that represent different parts of a word problem, the point at which the lines intersect (where they cross) is your answer.

Here’s an example:

Jacob is exactly 5 years younger than Marnie, and together their ages add up to 15. How old are they?

To solve this problem, first make a chart to show that Jacob is 5 years younger than Marnie:


Then make another chart to show that together, the two children’s ages add up to 15:


Finally, plot both lines on a graph where the horizontal axis represents Jacob’s age and the vertical axis represents Marnie’s age:


Notice that the two lines cross at the point where Jacob is 5 and Marnie is 10 years old, so these are the two children’s ages.

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