SOLUTION: Going into the final exam, which will count as 2/3 of the final grade, Larry has test scores of 86, 80, 84, and 90. What score does Larry need on the final exam in order to earn a

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Question 1208352: Going into the final exam, which will count as 2/3 of the final grade, Larry has test scores of 86, 80, 84, and 90. What score does Larry need on the final exam in order to earn a B, which requires an average score of 80? What does he need to earn an A, which requires an average score of 90?

To Earn a B:
(86 + 80 + 84 + 90 + B)/5 = 80
To Earn an A:
(86 + 80 + 84 + 90 + A)/5 = 90
What do you say about my setup?
Found 2 solutions by mccravyedwin, greenestamps:
Answer by mccravyedwin(407) About Me  (Show Source):
You can put this solution on YOUR website!

No, Larry's exam counts 2/3 and Larry's present average counts only 1/3.

Let x = the score Larry would need to make to just barely have a final score 
of 90, so he could make an A.
 



First, find Larry's present average.  

%2886+%2B+80+%2B+84+%2B+90%29%2F4+=+340%2F4+=+85

Then substitute and solve the equation

expr%281%2F3%29%2A%2885%29+%2B+expr%282%2F3%29%2A%28x%29%22%22=%22%2290

Multiply through by 3

85%2B2x%22%22=%22%22270

2x%22%22=%22%22185

x%22%22=%22%2292.5

So Larry would need to make at least 92.5 on his exam to get an A.

Now you do the same to figure what Larry would need to make on his exam

to just barely get a B.

Edwin

Answer by greenestamps(13200) About Me  (Show Source):
You can put this solution on YOUR website!


Your equations would only be right if the final exam counted only as much as each test. You need to weight the score on the final appropriately.

There are 4 test scores which count for 1/3 of the grade, and the final counts or 2/3 of the grade. Since the final counts twice as much as the 4 tests, the final has a weight equivalent to 8 tests (making 12 "tests").

So to answer the two questions by the method you are using, you could use the equations

(86+80+84+90+8A)/12 = 90

and

(86+80+84+90+8B)/12 = 80

That first equation will give you the same answer as shown by the other tutor using a different method. As he did, I leave it to you to solve the second problem to find the score needed to get a B.