Question 826285
<pre>
let x = the number of questions answered correctly, then:
180-x = the number of unattempted or wrongly answered questions.

Points earned for the x questions answered correctly = 4x
Points deducted from the 180-x unattempted or wrongly
      answered questions = -1(180-x).

4x - 1(180-x) = 450

 4x - 180 + x = 450
   
     5x - 180 = 450

           5x = 630

            x = 126

Number of questions answered correctly = 126
number of unattempted or wrongly answered questions = 180-126 = 54

Checking 

4×126 = 504 for 126 questions answered correctly
-1×54 = -54 for 54 unattempted or wrongly answered questions
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       450 = his score  (that checks!)

Edwin</pre>