SOLUTION: To get a grade of B in your course, you must average at least 75% on your exams. You have taken the first three exams and gotten scores of 68, 78, and 81. What must be your score o

Algebra ->  Average -> SOLUTION: To get a grade of B in your course, you must average at least 75% on your exams. You have taken the first three exams and gotten scores of 68, 78, and 81. What must be your score o      Log On


   

Question 884046: To get a grade of B in your course, you must average at least 75% on your exams. You have taken the first three exams and gotten scores of 68, 78, and 81. What must be your score on the last exam to get a B?
Answer by SmithWillSuffice(4) About Me  (Show Source):
You can put this solution on YOUR website!
We can do this algebraically as well as using trial and error. Trial & error is ok here because there are relatively few numbers to test, but for most of you it will be quicker using algebra.

So here's what you can do. The unknown x is the final exam percentage score, which could range from 0% to 100%. Immediately we might note mentally to ourselves that it could be the case that we might need x%3E100 to achieve an overall 75%. But this fear turns out to be unfounded, since already your average is +%2868%2B78%2B81%29%2F%283%29+=+227%2F3+=+75+%282%29%2F%283%29+. So to maintain an average above 75 you will not need a final exam score over 75.

So we will have a final overall grade from the average of the four exams, which we must equate to 75, so
+75+=+%2868%2B78%2B81%2Bx%29%2F%284%29+
thus +4+%2A+75+=+68%2B78%2B81%2Bx+
thus +300+=+68%2B78%2B81%2Bx+
thus +x+=+300+-+%2868%2B78%2B81%29
thus +x+=+300+-+227+
thus +x+=+73.+