i need help calculating my percentage

Question

i have a 64% average and my exam is coming up. If i get an 80% on my exam (exam worth 15% of final mark) what is my percentage going to be

Answer 1

This kind of average calculation is called a "weighted average."  The exam is worth 15% (that's its weight) and, we assume, the other 85% of the class work (that's its weight) has an average of 64%.  The total (for the denominator is 100%).  So, it looks like this:

                    [ (0.85*64) + (0.15)*80 ] / 100 = 66.4

Answer 2

I'm assuming you have completed the rest of your class work credit already at the 64% average. That means that 85% of your grade had an average of 64% (you could think about it as getting a 64 on 85 out a 100 assignments), and you plan to get an 80% on an exam that counts as 15% of your grade (like getting an 80 on only 15 assignments out the total 100). You multiply your grade by the percentage that each assignment counts for and then divide by 100. Example, 64 times 0.85 plus 80 times 0.15 then divide by 100. The answer is 66.4. The exam has too little pull to bring up your grade very much at this point. It could however pull down your grade if you get a lower grade on this exam than your current average. I would look for extra credit or bonus assignments if available to help pull up your grade as well as trying to get a good grade of the exam.