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Brain Teaser: How well do you understand weighted averages?
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December 9th, 2009
You have used weighted averages if you have ever tried to compute your grade in a class where regular tests and finals were weighed differently. Weighted averages show up in a wide variety of applications. Weighted averages for two quantities have some particularly nice properties.
The following problem came up in an online tutoring session. I solved it with the student using some messy algebra, because I suspected the student did not understand weighted averages. If you use weighted averages, this particular problem is set up so it can be solved fairly easily without any algebra. Do you see how to do it? Also let me know if you were ever taught in school about weighed averages.
How much of a 2% solution of sulfuric acid must be used to dilute 5 liters of a 10% solution to get a 7% solution?
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