The percent of students that are aged 19 years or more is determined as 84%.
In a normal distribution curve 1 standard deviation below the mean is defined as follows;
M - d = 20.6 yrs - 1.3 yrs = 19.3 years ≈ 19 years
19 years or more will occur at (M - d) + (M) + (M + 2d) = 100% - (M - d)
= 100% - 16%
= 84%
Thus, the percent of students that are aged 19 years or more is determined as 84%.
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