The formula for the z score of a number is given by:
[tex]z=\frac{x-\overline{x}}{\sigma}[/tex]Where:
[tex]\begin{gathered} x=\text{ the observed value} \\ \overline{x}=\text{ the mean} \\ \sigma=\text{ the standard deviation} \end{gathered}[/tex]In this case,
[tex]\begin{gathered} x=75 \\ \overline{x}=71 \\ \sigma=\text{ 3.5} \end{gathered}[/tex]Therefore, the z score of x=75 is given by:
[tex]z=\frac{75-71}{3.5}=\frac{4}{3.5}\approx1.143[/tex]Therefore, the probability that a boy is taller than 75 inches is given by the area under the normal probability distribution curve between z=1.143 and z=∞, P(z > 1.143):
The area is approximately 0.1265.
Therefore, the required probability is 0.1265.
Convert the probability to percent by multiplying with 100:
[tex]0.1265\times100=12.65[/tex]Hence, about 12.65 % of all the boys are taller than 75 inches.
Therefore, the total number of boys that are taller than 75 inches is given by:
[tex]\frac{12.65}{100}\times1707\approx216[/tex]Therefore, the number of boys expected to be taller than 75 inches is approximately:
216
