marks: calculating score needed on exam to get....

[Guest]

If i got 75% in class, worth 70% of my overall mark, what do i need to get on the exam, worth 30%, to get finish with 81%? Can someone pleas show me how to calculate this so i know what to aim for on the exam?

Thanks

 

[stapel]

Here is one way of calculating this sort of exercise:

* You got 75% of the first 70 points. How many points is that?

* You want 81% of the total 100 points. How many points is that?

* Given the points you already have and the total points you need, how many points do you need to get on the exam?

* The exam is worth 30 points. What percentage of this thirty points is represented by the additional number of points you need?

If you get stuck, please reply showing how far you have gotten in following these steps. Thank you.

Eliz.

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Edit: Ne'mind: Complete solution is posted below.

 

[soroban]

Hello, Aka!

I'm going to drop the extra percent-signs
\(\displaystyle \;\;\) and treat your scores as whole numbers.

If i got 75 in class, worth 70% of my overall mark,
what do i need to get on the exam, worth 30%, to get finish with 81?

This is a "weighted average" problem, where the scores do not have equal "weight".

Your classwork is worth 70% while your exam is worh only 30%.


Let \(\displaystyle E\) = your exam score.

Your average is: \(\displaystyle \,(\text{70% of Classwork})\,+\,(\text{30% of Exam}) \;= \;(0.70)(75)\.+\.(0.30)E\)

Since you want your average to be 81: \(\displaystyle \,(0.70)(75)\,+\,0.30E\:=\:81\)

Solve for \(\displaystyle E:\;\;52.5 \,+\,0.30E\:=\:81\;\;\Rightarrow\;\;0.30E\:=\:28.5\;\;\Rightarrow\;\;E\:=\:\frac{28.5}{0.30}\:=\:95\)

You will need a 95 on the exam to have a final average of 81.