A weighted average takes into account the proportional value of each test, rather than treating each test equally. For example, consider a situation where you got an 80% on a lecture exam and a 90% on a practicum. Since, in ZOO 200, a lecture exam is worth 1.75 times that of a lab exam, the weighted average of the two tests would be
(.90 + (1.75)(.80))/(1.0 +1.75) or 83.6%.
Because the final is worth 2.25 times the lab practicum, if you got an 80% on the final exam and a 90% on the last practicum the weighted average would be
((.90 + (2.25)(.80))/(1.0 +2.25) or 83.1%
If the tests were of equal value, the average would simply be (.90 + .80)/2 or 85%.