# Math equation problem

May 28, 2015 5:31 AM Subscribe

Asking for a friend:
I have a question about how to work out a student's exam mark.
Unit 1 is worth 60%, Unit 2 is worth 40%. Both units are marked out of 80. For example, a student scores 67/80 on unit 1 and 69/80 on unit 2. What is their overall mark?
Thanks for any help!

Yup! What stripesandplaid said.

posted by math at 5:35 AM on May 28, 2015 [2 favorites]

posted by math at 5:35 AM on May 28, 2015 [2 favorites]

Best answer: 0.6 * (67/80) + 0.4 * (69/80) = 84.75%

posted by TORunner at 5:35 AM on May 28, 2015 [2 favorites]

posted by TORunner at 5:35 AM on May 28, 2015 [2 favorites]

And to be clear, AugustWest's solution is also correct and is the same as stripesandplaid.

posted by math at 5:36 AM on May 28, 2015 [2 favorites]

posted by math at 5:36 AM on May 28, 2015 [2 favorites]

And TORunner. OK, we can stop now.

posted by math at 5:36 AM on May 28, 2015 [2 favorites]

posted by math at 5:36 AM on May 28, 2015 [2 favorites]

Just in case the process is unclear, many people would solve this by

If you have two sets of fractions that need to be equal to each other:

67/80 and ?/60

then you can multiply 67 and 60 (which gives you 4020)

and divide that answer by 80 to get the ? (which gives you 50.25)

You would need to do the same thing with the relevant numbers for unit 2.

69/80 and ?/40

(That's 69 times 40 which is 2760, divided by 80, which is 34.5)

Put both results of cross multiplying together (50.25 and 34.5) to get the results for the exam.

posted by eisforcool at 6:07 AM on May 28, 2015 [1 favorite]

**cross multiplying**.If you have two sets of fractions that need to be equal to each other:

67/80 and ?/60

then you can multiply 67 and 60 (which gives you 4020)

and divide that answer by 80 to get the ? (which gives you 50.25)

You would need to do the same thing with the relevant numbers for unit 2.

69/80 and ?/40

(That's 69 times 40 which is 2760, divided by 80, which is 34.5)

Put both results of cross multiplying together (50.25 and 34.5) to get the results for the exam.

posted by eisforcool at 6:07 AM on May 28, 2015 [1 favorite]

Best answer: And for future reference, the googlable keywords you are looking for are "Weighted average" or "weighted mean."

posted by If only I had a penguin... at 6:14 AM on May 28, 2015 [4 favorites]

posted by If only I had a penguin... at 6:14 AM on May 28, 2015 [4 favorites]

If you don't require the answer to be "over 80," you could make it over 400. It's basically the same as what people have suggested. Add (3 times unit 1's score) to (2 times unit 2's score).

posted by halifix at 12:50 PM on May 28, 2015

posted by halifix at 12:50 PM on May 28, 2015

This thread is closed to new comments.

posted by stripesandplaid at 5:34 AM on May 28, 2015 [2 favorites]