<p>Here is a Level 2 question where this last strategy is effective:</p>
<p>If x+7y=15 and x+3y=7, what is the value of x+5y?</p>
<p>Note that this question can be solved in several different ways:</p>
<p>(1) Guessing and checking until you find x and y.
(2) Solving algebraically for x and y by using elimination, substitution, or Gauss Jordan reduction.
(3) Using MATRIX functions in your calculator to solve by Gauss Jordan reduction.
(4) Finding the point of intersection of the graphs of the two equations.
(5) Trying a simple operation</p>
<p>I believe that (5) is the quickest and easiest method in this case.
(3) Sol</p>