Question

A college student completed some courses worth 3 credits and some courses worth 4 credits. The student earned a total of 59 credits after completing 18 courses.
How many courses worth 2 credits did the student complete?

Answer 1

Answer:

He completed 13 courses worth 3 credits and 5 courses worth 4 credits.

Step-by-step explanation:

Let

Number of courses worth 3 credits = x

Number of courses worth 4 credits = y

1. The student completed a total of 18 courses, then

$x+y=18$

2. The student earned a total of 59 credits, he earned 3x on 3 credits' courses and 4y on 4 credits' courses, so

$3x+4y=59$

3. You get the system of two equations:

$\left\{\begin{array}{l}x+y=18\\ \\3x+4y=59\end{array}\right.$

From the first equation

$x=18-y$

Substitute it into the second equation:

$3(18-y)+4y=59\\ \\54-3y+4y=59\\ \\4y-3y=59-54\\ \\y=5\\ \\x=18-5=13$

He completed 13 courses worth 3 credits and 5 courses worth 4 credits.