SOLUTION: I do not have the ISBN # because my chapter is printed off since I am going to school on-line. I would appreciate some help on this problem please. Sam must have an average of 70

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Question 112744: I do not have the ISBN # because my chapter is printed off since I am going to school on-line. I would appreciate some help on this problem please.
Sam must have an average of 70 or more on his summer course to obtain a grade of C. His first three test grades were 75, 63, and 68. Write an inequality representing the score that Sam must get on the last test to get a C grade.
I believe that the answer is a 69 for the final score. What I did was added the 3 scores and divided by 3, I hope this was right but I am unsure how to write it into an inequality.
Thank You,
Barb Neely
Answer by mathnard(10) About Me  (Show Source):
You can put this solution on YOUR website!
Let's check your answer... let's average the 4 test scores now, including the 69 that you are guessing for the last test score :
%2875%2B63%2B68%2B69%29%2F4=68.75
68.75 is not a C, so it looks like we will have to re-think this problem.

You actually need to average 4 numbers if you want to set up the inequality correctly. You have the first the grades AND the unknown last grade (x)...and then divide by 4 and THIS should be greater than 70...
%2875%2B63%2B68%2Bx%29%2F4%3E70

Now, let's multiply both sides by 4:
The fours will cancel out on the left side, but not on the right side...
75%2B63%2B68%2Bx%3E280

Let's add the numbers together on the left-hand side:
206%2Bx%3E280

And finally, let's subtract 206 from both sides:
x%3E74

Really, it should be that x is greater than or EQUAL to 74 if the student wants to reach a grade of 70 or better.