Question

An engineer wishes to determine the width of a particular electronic component. If she knows that the standard deviation is 1.2 mm, how many of these components should she consider to be 90% sure of knowing the mean will be within ±0.3 mm?

• 63
• 7
• 27
• 12
• 44

Answer 1

Given that,

standard deviation =s =   =1.2

Margin of error = E = 0.3

At 90% confidence level

= 1 - 90%  

= 1 - 0.90 =0.10

/2 = 0.05

Z/2 = Z0.05 = 1.645

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

n = ( 1.645 *1.2 / 0.3 )2

n =44

Sample size = n =44