<p>Suppose I got B+ in a 4 unit class, A- in a 3 unit class, and an A in another 3 unit class. Since rider730 kindly mentioned add 0.3 for + and subtract 0.3 for -, my GPA becomes</p>
<p>(3.3<em>4 + 3.7</em>3 + 4.0*3) / (4+3+3) = 3.68</p>
<p>Tell me if you still don’t get it.
You can tell the 4-unit class has a higher impact on my GPA.</p>