To find for the value of the approximate width or margin of error, we make use of the following formula:
approximate width = ± z [p (1 – p) / n]^0.5
where,
z = z score can be obtained using normal distribution tables at 90% confidence level
p = probability of success
n = number of samples = 25
Using the standard distribution tables, the value of z at 90% level is:
z = 1.645
The probability of success is 12 out of 25, therefore:
p = 12 / 25 = 0.48
Therefore the approximate width is:
approximate width = ± 1.645 [0.48 (1 – 0.48) / 25]^0.5
approximate width = ± 1.645 (0.0999)
approximate width = ± 0.164
