Question

Suppose you are designing a sample to find the mean age for young adults who commit crimes, with a maximum error of one year, with 99% of confidence level. If we know that population standard deviation is 3 years, the smallest sample size that you need is almost:

A) 60

B) 35

C) 25

D) 81

Answer 1

Solution :

Given that,

standard deviation = = 3

margin of error = E = 1

At 99% confidence level the z is ,

  = 1 - 99% = 1 - 0.99 = 0.01

/ 2 = 0.01 / 2 = 0.005

Z_/2 = Z_0.005 = 2.576

Sample size = n = ((Z_/2 * ) / E)²

= ((2.576 * 3) / 1 )²

= 60

Sample size = 60

Option A ) is correct.