Answer: 82%
Step-by-step explanation: 68% ? of the distribution lies within one standard deviation of the mean. ? about 95% is within 2 stdv.
So add and subtract 12 to each side of the mean. This will get you the interval of 298 to 322.
286 + 12 = 298 so another standard deviation on the lower side of the interval is needed.
Subtract the 1 stdv from 2 stdv to find how much more of the data 2 stdvs includes.
95% - 68% = 27%
Divide 27% by 2 because we only need the left.
27% ?2 = 13.5%
Finally add 13.5% to 1 stdv to get the total.
13.5% + 68% = 81.5% for the interval from 286 to 322.
Rounded to 82%.
