The other thing to place into the equation is the type of classes you are taking.
Physics could be a 4.0 credit since it has a lab, while Lit is a 3.0. They are all on a 4.0 scale, but the credit scale can vary. I also know that for even our DS and DD at 2 different colleges, they both have some classes on a 7 pt scale and some a 10 pt scale. 92 is not necessarily an A for every class.
Let's say you have 16 credits
Physics 4.0 - C = 4.0 X 2.0 = 8.0
Lit 3.0 - B = 3.0 X 3.0 = 9.0
Calc - 4.0 C = 4.0. x 2.0 = 8.0
History - 3.0 -B = 3.0 X 3.0 = 9.0
French-3.0 - B = 3.0 X 3.0 = 9.0
Your total would be 43.0 divide by 17 credits. That is your gpa. 2.53. Now if you just took 5 classes and the (13 gpa pts) your gpa would have been 2.6.
The best weigh to determine your true gpa is to multiple the % in the class by the credits. Add them all up, and divide the number by the total of classes. That is probably the system they are using.
Some schools will even take it a notch further by giving different weight for A+, A, A-.