Take the 2-minute tour ×
Mathematics Stack Exchange is a question and answer site for people studying math at any level and professionals in related fields. It's 100% free, no registration required.

I've done a search for the answer but still couldn't figure it out.

Say for example:

Year 1 Result = 80% (Weight:20%)

Year 2 Result = 70% (Weight:10%)

Year 3 Result = Unknown (Weight:70%)

I've not yet got my results for year 3. I want to calculate what my average percentage is so far, based on year 1 and 2 and what I would need to achieve in my 3rd year with a weighting of 70%.

Thanks.

share|improve this question
    
What are you trying to get? I assume you are trying to weigh grades in a class or something and trying to find out what you need on Year 3 to get a certain grade in the class. If you provide what you are trying to get we can help. –  Dan W Oct 17 '11 at 18:48
    
I'm trying to achieve a 70% average across 3 years with those weightings. Thanks –  Henryz Oct 17 '11 at 18:54

2 Answers 2

Imagine there are 100 points available, 20 of them in year 1, 10 in year 2, and 70 in year 3. You got 80% of 20=16 in year 1 and 70% of 10=7 in year 2. So now you have 23 and need 70. You need 47, which is about 67% of 70.

share|improve this answer

Since you are trying for $70\%$ total, you equation looks like:

$$0.7 = 0.8*0.2 + 0.7*0.1 + x*0.7$$

Then, when you solve for $x$, you get:

$$x = 0.67$$

Meaning, you need to get a $67\%$ on Year 3 Result to get $70\%$ for all three years.

share|improve this answer

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.