Question

An engineer wishes to determine the width of a particular electronic component. If she knows that the standard deviation is 1.9 mm, how many of these components should she consider to be 90% sure of knowing the mean will be within ±0.5±0.5 mm?

• 7
• 40
• 24
• 19
• 142

Answer 1

Given that,

standard deviation =s =   =1.9

Margin of error = E = 0.5

At 90% confidence level

= 1 - 90%  

= 1 - 0.90 =0.10

/2 = 0.05

Z/2 = Z0.05 = 1.65

sample size = n = [Z/2* / E] 2

n = ( 1.65 * 1.9 / 0.5 )2

n =40

Sample size = n =40