In: Statistics and Probability
Of 50 bank customers depositing a check, 17 received some cash back.
(a) Construct a 90 percent confidence interval for the proportion of all depositors who ask for cash back. (Round your answers to 4 decimal places.)
The 90% confidence interval is from to
Solution :
Given that,
n = 50
x = 17
Point estimate = sample proportion = = x / n = 17/50=0.34
1 - = 1- 0.34 =0.66
At 90% confidence level
= 1 - 90%
= 1 - 0.90 =0.10
/2
= 0.05
Z/2
= Z0.05 = 1.645 ( Using z table )
Margin of error = E Z/2 *(( * (1 - )) / n)
= 1.645 *((0.34*0.66) / 50)
E = 0.1102
A 90% confidence interval for population proportion p is ,
- E < p < + E
0.34-0.1102 < p <0.34+ 0.1102
0.2298< p < 0.4502
The 90% confidence interval for the population proportion p is : 0.2298, 0.4502