If you make an average of 78 on your last seven exams how high would you have to score to obtain an 80 average?

you would need a 94. Multiply your current average of 78 times 7 to get to 546. To have an average of 80, you multiply 80 *8 to get 640. 8 represents the total number of exams you have taken. I am assuming the question is "what does the student need to score on his eighth exam to get an 80 for the semester?" subtract 546 from 640 and you get 94.