Question

A survey states that 280 out of 800 people smoke on a regular basis. Determine the required sample size if you want to be 90% confident that the sample proportion is within 3% of the population proportion.

Answer 1

Solution :

Given that,

= 280/800=0.35

1 - = 1 - 0.35 = 0.65

margin of error = E = 3% = 0.03

At 90% confidence level

= 1 - 0.90 = 0.10

/2 =0.05

Z/2 = 1.645 ( Using z table )

Sample size = n = (Z/2 / E)2 * * (1 - )

= (1.645 / 0.03)2 * 0.35 * 0.65

Sample size = 1619