Sample Size = n = 30
Number of smartphone users = x = 12
Proportion of smartphone users = p = x/n = 12/30 = 0.4
Confidence interval = 96%
Z-value for confidence interval = 2.054
Error term of the interval is given by:
![E = z \sqrt{ \frac{p(1-p)}{n} } \\ \\ E=2.054 \sqrt{ \frac{0.4(0.6)}{30} } \\ \\ E=0.184 ](https://tex.z-dn.net/?f=E%20%3D%20z%20%5Csqrt%7B%20%5Cfrac%7Bp%281-p%29%7D%7Bn%7D%20%7D%20%5C%5C%20%20%5C%5C%20%0AE%3D2.054%20%5Csqrt%7B%20%5Cfrac%7B0.4%280.6%29%7D%7B30%7D%20%7D%20%5C%5C%20%20%5C%5C%20%0AE%3D0.184%20%0A%20)
The 96% confidence interval will be p <span>± E .
p - E = 0.4 - 0.184 = 0.216
p + E = 0.4 + 0.184 = 0.584
Therefore, the 96% confidence interval will be (0.216, 0.584)</span>