Standard Deviation Questions

Submitted by mlmPMP2013 on Wed, 05/08/2013 - 19:26

Hi All -- need help with the following question.

If you know the expected value is 500 and the standard deviation is 12, you can say with approximately a 95 percent confidence rating which of the following?

  1. Add a note hereThe activity will take from 488 to 512 days.

  2. Add a note hereThe activity will take from 464 to 536 days.

  3. Add a note hereThe activity will take from 494 to 506 days.

  4. Add a note hereThe activity will take from 476 to 524 days.

The answer is D, what i don't understand is you have to multiple the Standard Deviation providedby 2, why?

Thanks!

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crushPMP's picture

crushPMP

Wed, 05/08/2013 - 20:32

 95% is 2 SD

So 500 +- 24 is the answer

476, 524 - And D

I am a stats major and I would love 1 75 such questions on the exam :-)

mlmPMP2013

Wed, 05/08/2013 - 20:45

 Oh so does that mean for 3 standard deviation you multiply by 3?

crushPMP's picture

crushPMP

Wed, 05/08/2013 - 20:47

 Yes

mlmPMP2013

Wed, 05/08/2013 - 21:18

 That really helps thanks!  Good luck with ur studying!

rwmv

Thu, 05/09/2013 - 03:19

 I didn't quite understand. Could please explain how to solve this problem?

Thanks