Since 65 is the mean, its z-score is 0.
Find the z-score of 67
, round to 0.67
Find z = 0.6 and go across to the column with 0.07
and read either 0.2486 or 0.7486.
If you read 0.2486, that's the answer because you table
reads area from 0 to the right.
If you read 0.7486, you must subtract 0.5 and get 0.2486,
because your table reads areas from the far left side.
That's the area under the curve between the two green lines:
If you use a calculator, you will get a more accurate
answer.
mormalcdf(0,0.666667)
Get 0.2475.
The discrepancy is because tables are not as accurate as
calculators.
In fact, when you use a calculator you do not need to calculate
the z-score, just put the lower and upper limits followed by the mean
and standard deviation.
mormalcdf(65,67,65,3)
That gives 0.2475, also.
Edwin
