Answer:
[tex]Mean=79[/tex]
[tex]\sigma=30.3951.[/tex]
Step-by-step explanation:
From the question we are told that:
[tex]Age Bracket :19-20[/tex]
[tex]5th\ percentile = 42[/tex]
[tex]50th\ percentile = 79[/tex]
[tex]95th\ percentile = 142.[/tex]
Generally the mean Median and mode of the 50th percentile is are all equal
[tex]Mean=Median=Mode[/tex]
Therefore
[tex]Mean=79[/tex]
Generally for Normal distribution
[tex]5th\ percentile\ = mean - 1.645*\sigma[/tex]
[tex]95th\ percentile\ = mean + 1.645*\sigma[/tex]
Therefore
[tex](95th\ percentile\ - 5th\ percentile) = 2*(1.645*SD).[/tex]
[tex]\sigma=(95th\ percentile\ - 5th\ percentile)/3.29[/tex]
[tex]\sigma=\frac{142-42}{3.29}[/tex]
[tex]\sigma=30.3951.[/tex]