percentage question

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January 12th 2009, 12:50 PM
Sky MacKenna

percentage question

Revewing for college math placement test that expired after a year and need to retake it. so working on practice tests till i can fully be comfortable. I am horrible at math, and always have to keep relearning. It's always been my hardest subject.

"Mary has taken three tests with grades of 58%, 62%, and 64%. What does she need to score on test 4 to average exactly 68% on all four tests?"

I've tried putting the percentages in my calculator as decimals and adding them ".58+.62+.64=1.84"

I've tried putting the percentages in my calculator as decimals and dividing them ".58/.62/.64=1.461693548"

" " multiplying them ".58*.62*.64=.230144"

I know subtracting them would lead to nothing.

I've tried putting the percentages as decimals, adding them and diving by 4} ".58+.62+.64/4=1.36"

I've done "((58/100)(62/100)(64/100))/4=.46"

I can't seem to remember how to work the problem and get the right answer.

***Thank you so much for taking the time to read my post and returning any advice on my problem at hand! =D
January 12th 2009, 02:59 PM
stapel

Quote:

Originally Posted by Sky MacKenna

"Mary has taken three tests with grades of 58%, 62%, and 64%. What does she need to score on test 4 to average exactly 68% on all four tests?"

Let each test be worth a hundred points. How many points does she have so far?

How many points are possible (assuming perfect scores on everything) on the four tests together?

If she wants 68% overall, how many of those points must she earn?

Given her current point total and her desired point total, how many more points does she need?

Then what percentage does she need on the last test?

Have fun! :D
January 12th 2009, 03:22 PM
mr fantastic

Quote:

Originally Posted by Sky MacKenna

Revewing for college math placement test that expired after a year and need to retake it. so working on practice tests till i can fully be comfortable. I am horrible at math, and always have to keep relearning. It's always been my hardest subject.

"Mary has taken three tests with grades of 58%, 62%, and 64%. What does she need to score on test 4 to average exactly 68% on all four tests?"

[snip]

Solve $\frac{58 + 62 + 64 + x}{4} = 68$ for $x$ (assuming all tests carry equal weight).