In: Statistics and Probability
In a simple random sample of 70 automobile dealers registered in a certain state, 30 of them were found to have emission levels that exceeded a state standard. At the 95% confidence interval, the proportion of automobiles whose emissions exceeded the state standard is closest to
Solution :
Given that,
n = 70
x = 30
Point estimate = sample proportion = = x / n = 30/70=0.429
1 - = 1- 0.429 =0.571
At 95% confidence level the z is ,
= 1 - 95% = 1 - 0.95 = 0.05
/ 2 = 0.05 / 2 = 0.025
Z/2 = Z0.025 = 1.96 ( Using z table )
Margin of error = E = Z/2 * ((( * (1 - )) / n)
= 1.96 (((0.429*0.571) /70 )
E = 0.1159
A 95% confidence interval for population proportion p is ,
- E < p < + E
0.429-0.1159 < p <0.429+ 0.1159
0.3131< p < 0.5449
The 95% confidence interval for the population proportion p is : 0.3131,0.5449