Algebra Equation Assistance

[TheRundownRabbit]

I need to write an equation that...um...okay, I have 3 grades, they are worth 25%, 30%, and 20% in the overall course grade, the final is worth 25%. What I need to do is write an equation which, given the first 3 grades, will give me what I need to make on the final grade to receive a 70% for the entire course. This is for one of my C++ Programming projects and the algorithm I have right now isn't giving me a proper answer.

What I have for the equation right now is "final = ( .70 - ( .20 * midterm ) - ( .30 * project ) - ( .25 * paper ) ) / .25"

I think I am missing something and my brain is just completely...blegh right now

 

[Batou667]

If your first three grades are A,B,C and your last one is D, then the threshold (minimum permissible) mark for D is

D = 280 - A - 1.2B - .8C

I plugged in some numbers and it seems to work OK. If you got 60% for A, B and C, for example, then you'd need 100% in D to get 70% overall.

Hope this helps, and that I haven't made any mistakes!

 

[dmase]

I believe you need to make these changes.

final = ( 70 - ( .20 * midterm ) + ( .30 * project ) + ( .25 * paper ) ) / .25

if midterm, project, and paper are all 50 then you'd need a 130 on the final to get 70. If you plug 80 into midterm project and paper you get a 40 for the final. Also batou gave a correct answer as far as I can tell.

 

[The_Great_Galendo]

Your original formula seems fine to me. I mean, we have

.20*midterm + .30*project + .25*paper + .25*final = .70
.25*final = .70 - .20*midterm - .30*project - .25*paper
final = (.70 - .20*midterm - .30*project - .25*paper) / .25

which is precisely what your original equation says. What was the problem with your original evaluation?

 

[SeaCalMaster]

Your original formula seems fine to me. I mean, we have

.20*midterm + .30*project + .25*paper + .25*final = .70
.25*final = .70 - .20*midterm - .30*project - .25*paper
final = (.70 - .20*midterm - .30*project - .25*paper) / .25

which is precisely what your original equation says. What was the problem with your original evaluation?

Seconding this. I'm not sure why you think you got it wrong.