statistics
posted by D on .
In a survey of 400 college students, 40 were lefthanded. 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?

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.