Question

In a survey of 400 college students, 40 were left-handed. Treating the sample as if it were random and using 0.015 as the standard deviation of the sampling distribution of the sample proportion, what is the lower bound of a 95% confidence interval for the population proportion?

Answer 1

Use a proportional confidence interval formula:

CI95 = p + or - (1.96)(0.015)
...where p = x/n
Note: + or - 1.96 represents 95% confidence interval.

For p in your problem: 40/400 = .1

I let you take it from here to calculate the interval.