If X~N(12.4, variance^2) and 95% of the data lie in the interval 11.8 – 13.0, the standard deviation equals:
a) 1.2
b) 0.3
c) 0.09
d) 0.06
PLEASE HELP with this standard deviation question?
95% lies between [-2,2] ....
(13.0 - 11.8) / 4 ..... (2 sd's to the left of mean .. 2 to the right)
=(13.0 - 11.8) /.3
answer is B
Reply:I get b)
The z value corresponding to a 95% interval is 1.96, from a Normal table.
Z = (x-mean)/SD = (13-12.4)/SD
(13-12.4)/SD = 1.96
SD = .3 (rounded)
Reply:b
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