# Thread: standard deviation

1. ## standard deviation

Some reason I get a different answer than the actual answer.

* = Standard Deviation, which is unknown and that is what we are solving for

2. Originally Posted by freudling
Some reason I get a different answer than the actual answer.

* = Standard Deviation, which is unknown and that is what we are solving for
$\displaystyle 0.20 = \frac {[0.08 + (0.13 + 0.08)]SD}{0.25}$ ..............multiply both sides by 0.25

$\displaystyle \Rightarrow 0.05 = [0.08 + 0.13 + 0.08]SD$ .............calculate the coefficient of SD

$\displaystyle \Rightarrow 0.05 = 0.29SD$ ...................................Now divide both sides by 0.29

$\displaystyle \Rightarrow SD = \frac {0.05}{0.29} = 0.1724 ...$

3. Answer should be .6, but I can't quite get it.

4. Originally Posted by freudling
Answer should be .6, but I can't quite get it.
0.6 is not the solution to the equation you posted. double check for typos

5. Sorry, my error in posting, it is:

.20 = .08+ [(.13 - .08) * / .25] = .08+ .2 *

* = .12/.2 = .6

6. Originally Posted by freudling
Sorry, my error in posting, it is:

.20 = .08+ [(.13 - .08) * / .25] = .08+ .2 *

* = .12/.2 = .6
ok, so here we can cut out the middle man, and equate the first and last piece, we can do that since all three pieces are equal. i don't know how you ended up with this type of equation to begin with

$\displaystyle 0.20 = 0.08 + 0.2~SD$ ...........subtract 0.08 from both sides

$\displaystyle \Rightarrow 0.12 = 0.2~SD$ ........divide both sides by 0.2

$\displaystyle \Rightarrow SD = \frac {0.12}{0.2} = 0.6$

EDIT: Oh, the last piece is what you simplified the middle piece to get. Ok. Yeah, you still do what I did for the next step

7. Jhevon, you are the man. Thanks.