<PRE><B>Question 1104034</B>
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</PRE>