The mean of a normal probability distribution is 380; the standard deviation is 55. Refer to the table in Appendix B.1. (Round the final answers to 2 decimal places.)
a. About what percentage of the observations lie between 325 and 435?
Percentage of observations %
b. About what percentage of the observations lie between 270 and 490?
Percentage of observations %
c. About what percentage of the observations lie between 215 and 545?
Percentage of observations %
According to empirical rule, 68%, 95% and 99.7% of data lies within 1, 2 and 3 standard deviations of mean respectively.
Mean = 380
Standard deviation = 55
a) 380 - 1x55 = 325
380 + 1x55 = 435
325 to 435 is within 1 standard deviation of mean.
About what 68% of the observations lie between 325 and 435
b) 380 - 2x55 = 270
380 + 2x55 = 490
270 to 490 is within 2 standard deviations of mean.
About what 95% of the observations lie between 270 and 490
c) 380 - 3x55 = 215
380 + 3x55 = 545
215 to 545 is within 3 standard deviations of mean.
About what 99.7% of the observations lie between 215 and 545
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