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Mr. McKay wrote an algebra test with a total of 15 questions consisting of multiple choice and short response style questions. Multiple choice questions, x, were worth 5 points each and short response questions, y, were worth 10 points each. There were 100 total possible points on the test. Write and graph a system of linear equations for this situation to determine the number of each type of question.

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reinhard10158

Step-by-step explanation:

x = number of multiple choice questions

y = number of short response questions

x + y = 15

5x + 10y = 100

=>

x + 2y = 20

let's subtract the first from the second equation :

x + 2y = 20

- x + y = 15

--------------------

0 y = 5

x + y = 15

x + 5 = 15

x = 10

to graph you need to consider both equations as linear functions. and you need to transform them into e.g. a slope intercept form : y = ax + b

a is the slope, b is the y- intercept.

x + y = 15

transforms to

y = -x + 15

this line goes e.g. through the points (0, 15) and (1, 14).

and

x + 2y = 20

transforms to

2y = -x + 20

y = -x/2 + 10

this line goes e.g through (0, 10) and (2, 9).

the crossing point of both lines is the solution and should therefore be the point (10, 5) as calculated above.

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