4.1.NORMAL DISTRIBUTION173 To nd an area under the normal curve using a calculator, rst identify a lower bound and an upper bound. Theoretically, we want all of the area to the left of 1.5, so the left endpoint should be -1. However, the area under the curve is nearly negligible when Z is smaller than -4, so we will use -5 as the lower bound when not given a lower bound (any other negative number smaller than -5 will also work). Using a lower bound of -5 and an upper bound of 1.5, we get P (Z < 1:5) = 0:933. J Guided Practice 4.15Find the area under the normal curve to right of Z = 2. 11 J Guided Practice 4.16Find the area under the normal curve between -1.5 and 1.5. 12 TI-84: Find a Z-score that corresponds to a percentile Use2ND VARS,invNormto nd the Z-score that corresponds to a given percentile. 1.Choose2ND VARS(i.e.DISTR). 2.Choose3:invNorm. 3.LetAreabe the percentile as a decimal (the area to the left of desired Z- score). 4. Leaveas0andas1. 5.Down arrow, choosePaste, and hitENTER. TI-83: Do steps 1-2, then enter the percentile as a decimal, e.g.invNorm(.40), then hitENTER.
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