# Standard deviation help...

• Feb 14th 2010, 04:51 PM
WolfMV
Standard deviation help...
Hey all, I'm working on some homework for my business statistics class and ran into a question I'm having difficulties with. I couldn't find any similar examples and was hoping someone could explain the process to solve the question.

The question is . . .

The preparation time to mail envelopes with a weekly report to all executives in a company has a Normal distribution with a mean of 35 minutes and a standard deviation of 2 minutes. On 95% of such occasions the mailing preparation takes less than x minutes. What is the value of x?

I understand how to calculate the mean, how to use that to get the variance, and how standard deviation is the square root of variance. However I'm not sure how to apply all of that to a problem like this.

Thank you!
• Feb 14th 2010, 05:22 PM
aUSSIEuNDIES
Quote:

Originally Posted by WolfMV

The question is . . .

The preparation time to mail envelopes with a weekly report to all executives in a company has a Normal distribution with a mean of 35 minutes and a standard deviation of 2 minutes. On 95% of such occasions the mailing preparation takes less than x minutes. What is the value of x?

I understand how to calculate the mean, how to use that to get the variance, and how standard deviation is the square root of variance. However I'm not sure how to apply all of that to a problem like this.

Thank you!

Is this what you mean

SD-3 SD-2 Sd-1 SD0 SD1 Sd2 SD3

29min 31min 33min 35min 37min 39min 41min

\ 95%------------------------95% /

Therefore x = 39 min

Let me no if this is correct?