x~ N(1, .0004)
Find a value xc such that x will lie within x +/- xc 90% of the time.

Question

x~ N(1, .0004)
Find a value xc such that x will lie within x +/- xc 90% of the time.

amistre64 · Answer

if i read the notation right .. big if

this is saying a normal distribution with a mean of 1 and an sd of .0004 right?

amistre64 · Answer

is that "xc" part a typo?  or is it notationally significant to the problem?

anonymous · Answer

variance of .0004

anonymous · Answer

x subscript c as a value

amistre64 · Answer

variance, then sd is the sqrt of variance right?

anonymous · Answer

yes!

amistre64 · Answer

and you are wanting to determine the value of xc such that its pretty much a confidence interval of 90%

amistre64 · Answer

what is the z value of 45% from the mean?

anonymous · Answer

uhm .. i think so.

amistre64 · Answer

$$z=\frac{x-\bar x}{\sigma}$$
$$z\sigma+\bar x=x$$

amistre64 · Answer

$$z(\sqrt{.0004})+1=x$$when a z value of 45% from the mean is known from probably a z table

amistre64 · Answer

of course the x in my idea is a +- x since a zscore is symetric about the mean

anonymous · Answer

yeah ok, that makes sense.

anonymous · Answer

how would i find that z score? if i'm using the chart?

amistre64 · Answer

id need a ti83 or a z table to determine the proper z score :)

amistre64 · Answer

there are different charts and they tend to be author specific

amistre64 · Answer

you want to find .4500 in the field and line up the left and top values to get the zscore

amistre64 · Answer

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