SOLUTION: There were 15 questions in a Mathematics quiz. Cathy answered all 15 questions and scored 90 points . If 10 points were awarded for each correct answer and 5 points were deducted f

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Question 1104034: There were 15 questions in a Mathematics quiz. Cathy answered all 15 questions and scored 90 points . If 10 points were awarded for each correct answer and 5 points were deducted for each incorrect answer , how many questions did Cathy answer correctly ?
Answer by ankor@dixie-net.com(22740) About Me  (Show Source):
You can put this solution on YOUR website!
let r = the correct questions
let w = the wrong questions
there were 15 questions in a Mathematics quiz.
r + w = 15
Cathy answered all 15 questions and scored 90 points
If 10 points were awarded for each correct answer and 5 points were deducted for each incorrect answer ,
10r - 5w = 90
how many questions did Cathy answer correctly
:
Use eliminations with these two equations, multiply the 1st equation by 5
5r + 5w = 75
10r - 5w = 90
--------------Addition eliminates w, find r
15r = 165
r = 165/15
r = 11 questions answered correctly