How do you know how many correct answers doe's Noah have?

Question

A math exam consists of 20 questions. Every correct answer is given 5 points and 2 points are deducted for every wrong answer. Noah answered all the questions and got a score of 79. How many questions did he answer correctly?

Answer 1

Let x = # questions answered correctly.

y = # questions answered incorrectly

x + y = 20 (20 questions in total)

5x -2y = 79 (+5 points for each correct answer -2 points for each incorrect answer)

Solve the above system using either substitution ( y = 20 - x , for example), or addition/elimination (multiply 1st equation by -2 and add to the 2nd equation to eliminate y).

After solving, check your work here:

desmos.com/calculator/cbes6spzqf