3 variable equation? Please help!!!

Jun 2010
3
0
here it is:
(z)/[(y+21)/(x+5.5)]=(3.1)/(y/x)

I'm trying to find z. It's supposed to be my gpa so somewhere between 3.0 and 3.7 I have been at it for a long time. someone help me please, it's my first post!
 

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MHF Hall of Honor
Mar 2010
2,340
821
Chicago
here it is:
(z)/[(y+21)/(x+5.5)]=(3.1)/(y/x)

I'm trying to find z. It's supposed to be my gpa so somewhere between 3.0 and 3.7 I have been at it for a long time. someone help me please, it's my first post!
What are x and y? You can solve for z in terms of x and y, but you won't be able to say it's a number between 3.0 and 3.7 unless you can plug in x and y.
 
Jun 2010
3
0
I don't have X or Y. I just know it falls into that range because my GPA was a 3.1 at the end of the year and I got 4 A's and 2 B's, so it should've gone up.
 

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MHF Hall of Honor
Mar 2010
2,340
821
Chicago
I don't have X or Y. I just know it falls into that range because my GPA was a 3.1 at the end of the year and I got 4 A's and 2 B's, so it should've gone up.
You won't be able to solve in this manner without more information. GPA's are calculated by taking [sum of ((course grade value) * (course credit hours))] / (total credit hours), so it's a weighted average. For example, if biology is worth 3 credit hours and chemistry is worth 2, then an A (4.0) in biology will count more towards the GPA than an A in chemistry. And even if all your courses have the same credit hours, it's still true that: the more accumulated credit hours that went into your GPA of 3.1, the less your newer grades will affect your GPA (because the previous GPA's weight will be large compared with the weights of the new courses).

If you need an illustration:

The average of (1,4,3) is 8/3 \(\displaystyle \approx\) 2.67. If you add on another 4, then you have the average of (1,4,3,4) is 3. (It changed substantially.)

The average of (1,4,3,4,1,2,3,4,2,3,4,1,2,3,2,3,1,4,4,4,2) is 19/7 \(\displaystyle \approx\) 2.71. Adding on another 4, the average of (1,4,3,4,1,2,3,4,2,3,4,1,2,3,2,3,1,4,4,4,2,4) is 61/22 \(\displaystyle \approx\) 2.77. (It did not change very much.)
 
Jun 2010
3
0
Ok well, I have a 3.1 gpa. I received 5.5 credit hours this year and I got a 21 total for my grades. (3*4 a's + 3*3 B's = 21) Am I able to calculate my current cumulative GPA now? I know my current for this year is 21/5.5=3.82