Your math teacher tells you that the next test is worth 100 points and contains 38 problems. Multiple-choice questions are worth 2 points each and word problems are worth 5 points. How many of each type of question are there?​

If we assume that
x isthe number of multiple choice questions, and y is the number of word problems, we can write a system of equations like:
{ x + y = 38
{ 2x + 5y = 100

If we multiply the first equation by -2 we get:
{ -2x-2y = -76
{ 2x + 5y = 100

Now if we add both equations we get only equation with 1 unknown (y) :

3y = 24 ⇒ y = 8

Substituting the calculated value to the first equation we get:

x + 8 = 38 ⇒ x = 30

The solution:
{ x = 30
{ y = 8

means that:
The test had 30 multiple choice questions, and 8 word problems.

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