A college student completed some courses worth 3 credits and some courses worth 4 credits. The studentearned a total of 59 credits after completing 18 courses. How many courses worth 3 credits did the student complete?

The student completed 13 courses worth 3 credits

Step-by-step explanation:

System of Equations

Let's assign the following variables:

x = number of courses worth 3 credits

y = number of courses worth 4 credits

Some student completed 18 courses thus:

x + y = 18      [1]

The student earned a total of 59 credits:

3x + 4y = 59       [2]

From [1]:

y = 18 - x

Substituting in [2]:

3x + 4(18 - x) = 59

Operating:

3x + 72 - 4x = 59

Simplifying:

-x = 59 - 72 = -13

x = 13

The student completed 13 courses worth 3 credits

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