normal distribution SD question someone, problem, practice, question

dkishore1

on a practice problem I am having trouble with...the answer says 99% of observations fall w/in 3 SD of the mean. I had thought 99% of the observations fall w/in 2.575 SD of the mean...? Please someone clarify, it has been a very long day

Londonrocks

pg441
The key word is "Approximately":
Approximately 68% fall in +-1SD
Approximately 95% fall in +-2SD
Approximately 99% fall in +-3SD

ramzes

SD___________________Percentage in CI
-----------------------------------------------------------------------
1_______________________68.27

1.645___________________ 90%

1.96___________________ 95%

2 _____________________ 95.45%

2.576 ___________________ 99%

3 _____________________ 99.73%

4 _____________________ 99.99%

lc26mizzou

I thought that was a garbage question, too. I've memorized 90/1.65, 95/1.96, 99/2.58 and that's what I'm using on the exam.

Siddimaula

Turn to pg 326 in Volume 1 - CFA book.