# Thread: Standard deviation

1. ## Standard deviation need serious help

IM using my brothers account with his permission of course and so Im kinda stuck on these questions from 14 a)ii) downwards

thanks

2. Originally Posted by osmosis786
IM using my brothers account with his permission of course and so Im kinda stuck on these questions from 14 a)ii) downwards

thanks
I don't know about anyone else, but to me what you've attached is unreadable. Please type out your questions.

3. Originally Posted by mr fantastic
I don't know about anyone else, but to me what you've attached is unreadable. Please type out your questions.

I dont need someone to read my answers because i've tried to rub them out, unsuccessfully but i do need help with the questions asking for the standard deviation, and i think you will find that the actual questions are very readable:P

4. Originally Posted by osmosis786
I dont need someone to read my answers because i've tried to rub them out, unsuccessfully but i do need help with the questions asking for the standard deviation, and i think you will find that the actual questions are very readable:P
After some small effort I was able to read your questions. For future reference: When you want help from someone, you make things as easy as possible for that person. In this instance, that would mean typing your questions out.

14 a. (ii) Substitute the data into the usual formula that is sure to be in your notes and/or textbook.

14 b. Let X be the discrete random variable integers from 1 to 50. You're told that sd(X) = 14.43 => Var(X) = (14.43)^2.

You're expected to know that Var(aX + b) = a^2 Var(X) => sd(aX + b) = |a| sd(X).

(i) a = 1/2, b = 0.

(ii) a = -1, b = 0.

(iii) a = 1, b = 99.

5. I dont get what the '|a|' means thanks... and I dont get how to work it out...

6. Originally Posted by osmosis786
I dont get what the '|a|' means thanks... and I dont get how to work it out...
I have told you how to work it out. If you spent more than 5 minutes thinking about what I posted, then you might 'get how to work it out'.

|a| means the magnitude of a.

14 b. (i) The data is given by X/2 therefore sd = 1/2 sd(X) = 1/2 (14.43) = ....

(ii) The data is given by -X therefore sd = |-1| sd(X) = sd(X).

(iii) The data is given by X + 99 therefore sd = sd(X).