Solution :
Given that,
=
0.85
1 -
= 1 - 0.85 = 0.15
margin of error = E = 4% = 0.04
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 )
Sample size = n = (Z/2
/ E)2 *
* (1 -
)
= (1.96 / 0.04)2 * 0.85 * 0.15
= 306.12
=306 rounded
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