Quizzes $20\%$

Midterm $40\%$

Final $40\%$

Can someone please help me calculate what I have in the class so far? I'm pretty slow when it comes to numbers.

I'm getting the full $20\%$ from the quizzes. The midterm was out of $60$, and I got a $34$ :/

This is what I calculated. $56.6\%+20\%= 76.6 \%$ Is that right?

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(100 * 0.2 + 56.6 * 0.4)/60 = 42.64/60 ~ 71.066% – DavidP Jan 28 '14 at 19:40
Suppose you got 60 on the midterm. Your calculation would give you 100%+20%=120%. – vadim123 Jan 28 '14 at 19:45

Your current average (thus the expected total result if we assume that you perform euqally well in the final) is $$\frac{20+\frac{34}{60}\cdot 40}{20+40}=71.\overline1\,\%$$

If your final result is perfect, this will improve to $$\frac{20+\frac{34}{60}\cdot 40+40}{20+40+40}=92.\overline6\,\%$$ and if you completely fail at the final (and that doesn't invalidate the course by other reasons), you might drop down as far as $$\frac{20+\frac{34}{60}\cdot 40+0}{20+40+40}=42.\overline6\,\%$$

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A nice summary of my and fkraiem's answers. Thank you for clarifying both of our intents! :) – 2012ssohn Jan 28 '14 at 20:01
Minor(?) typo: the perfect-final number should be $82.6$, not $92.6$. – Barry Cipra Jan 28 '14 at 20:10

No, you got 56.7% of the 40% alloted to the midterm, so that's about 22.7%. You have 42.7% so far.

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Because you haven't taken your final yet (I assume), you have $60\%$ of your grades on record. We therefore have $$\frac{\frac{34}{60} \cdot 40 + 20}{\frac{60}{100}} \approx 71.1\%$$

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So I have a 71.1% in the class right now? – Adam Jan 28 '14 at 19:46
You have 71.1% of the points alloted so far, which amounts to a total of 42.7 as I said above. So you could either say that you have 71.1% or 42.7%, depending on how you look at it. 71.1% is a fairer estimate of your performance in the class so far, but 42.7% is a better estimate of how well you need to do on the final in order to pass the class. – fkraiem Jan 28 '14 at 19:53
For example, say the passing grade is 60%. Since you have 42.7% right now, you need to get 17.3% more. Since the final has 40% alloted to it, you need to get a score of 43.3% on the final. – fkraiem Jan 28 '14 at 19:56

Just to add a slightly different context...

If you have 100% quiz average (nice job!), then you can describe your final grade as

$$1 \cdot 20 + \frac{34}{60} \cdot 40 + x \cdot 40 = 42.67 + 40x,$$

where $0 \le x \le 1$ is the grade on your final.

Therefore, you have a lower bound of $42.67\%$, and an upper bound of $82.67\%$ for your class.

To obtain at least an $80\%$ final grade, you must get at least a $x = \frac{80-42.67}{40} = 93.3\%$ grade on your final exam.

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