A sample of concrete specimens of a certain type is selected, and the compressive strength of each specimen is determined. The mean and standard deviation are calculated as x = 4000 and s = 400, and the sample histogram is found to be well approximated by a normal curve.
(a)Approximately what percentage of the sample observations are between 3600 and 4400? (Round the answer to the nearest whole number.)
Approximately %
(b) Approximately what percentage of sample observations are outside the interval from 3200 to 4800? (Round the answer to the nearest whole number.)
Approximately %
(c) What can be said about the approximate percentage of observations between 3200 and 3600? (Round the answer to the nearest whole number.)
Approximately %