word problem, Im lost on how to set this up
posted by Carlos
Joe has scored 84, 89, and 90 on his first three exams in his math class. If the standard 70,80,90 scale is used for grades and the exams are equally weighted, what must he score on the final exam, f, in order to
a) Get a C average on exams?
f
b) Get a B average on exams?
f
c) Get an A average on exams?
f
< > or = to

Ms. Sue
84 + 89 + 90 = 263 points
400 = total possible points
0.7 * 400 = 280 needed for a C
0.8 * 400 = _____ needed for a B
0.9 * 400 = _____ needed for an A 
Carlos
sorry but I did not, I worked out what you posted and entered them in online and my answers were rejected.
ps. i didn't realize I could respond to you on this 
Ms. Sue
You didn't complete the problem.
For a C, 280 points are needed. Since Joe already has 263 points, he only needs 17 points on the last test for a C.
For a B, 320 points are needed.
320  263 = 57 needed
For an A  360 points are needed.
360  263 = ? 
Carlos
ahh now I see it! 17, 57, 97. not sure what I was thinking there. Thanks for your help!

Ms. Sue
You're very welcome.
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