Answer: 98
Step-by-step explanation:
Formula to find sample size if population standard deviation is known:
[tex]n=(\dfrac{z^c\times\sigma}{E})^2[/tex] , where [tex]\sigma=[/tex]population standard deviation, [tex]z^c[/tex] =Critical z-value for confidence level, E= Margin of error.
Given: [tex]\sigma=30,\ \ \ E=10[/tex]
Critical z-value for 90% confidence = 1.645
[tex]n=(\dfrac{1.645\times60}{10})^2\\\\=(1.645\times6)^2\\\\=9.87^2\\\\=97.4169\approx98[/tex]
Required minimum sample size = 98
