# Thread: Averages (Mean)

1. ## Averages (Mean)

I am trying to find the average of these test scores:

83

85

86

100 (this one is worth 25%, however)

I don't know how to do this because of the special one

2. ## Re: Averages (Mean)

What "special one"? You do know that 100/4= 25, don't you? If one is worth 25% then the other three must total 75%. And each one must be worth what?

3. ## Re: Averages (Mean)

Sorry, I meant that the the first three are worth a normal grade.

The last one is worth 25% of one of the first three.

4. ## Re: Averages (Mean)

I think I got it. Can someone verify?

$\displaystyle (.3125*83) + (.3125*85) + (.3125*86) + (.0625*100) = 85.6%$

5. ## Re: Averages (Mean)

No. If the last is worth 0.0625 and the others are worth four times as much, the others would be worth 4(0.0625)= 0.25, not 0.3125. And .25+ .25+ .25+ .0625 does not add up to 100%. I think you mistakenly took 1/4 of 1/4 to get 1/16 and the divided the remaining 15/16 by 3 to get 5/16 for each of the original three. You mistake was treating the first three as 1/4 each when you knew from the start that you were NOT dividing these equally.

Call the value of each of the first three "a" the last is worth "a/4". So we must have a+ a+ a+ a/4= 3a+ a/4= (12a+ a)/4= 13a/4= 1.00 so a= 4/13. each of the first tests is worth 4/13 and the last text is worth 1/4 of that, 1/13.

6. ## Re: Averages (Mean)

$\displaystyle (0.30769230769*83)+(0.30769230769*85)+(0.307692307 69*86)+(0.07692307692*100) = 85.8%$

There we go! Thanks!