Let Z be a standard normal random variable. Find the z-value(s) for the following situations.

a.) the area to the left of z is 0.2119

b.) The area betwen -z and z is 0.9030

c.) The area to the right of z is 0.6915

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- Oct 23rd 2007, 09:31 AM #1

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- Oct 23rd 2007, 01:48 PM #2

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This is an excersise in inverse table look up, and depends on what table you have.

Lets assume that you have a table of the cumulative standard normal, which

gives the area to the lef of z-values from 0 upwards, so these probabilities

are all greater than 0.5.

In a.) the probability is less than 0.5, so the z-score must be negative, so

we have to do an inverse look up for 1-0.2119=0.7881 then switch the sign

of the corresponding z-score. The z-score giving a p-value of 0.7881 is 0.8,

so the z-score we seek is -0.8.

RonL