These questions aren't that clear to me.
Are they talking about one-sided confidence intervals
OR the end points of a two-sided interval?
MY guess is the later, but at first I felt that these questions pertained to one-sided intervals.
IN 1. The mean wing span of a random sample of 35 birds is 186mm and the standard deviation is 28mm. Give the upper limit of a 90% confidence interval for the population mean wing span of birds, calculate using large-sanple methods.
you would calculate .
BUT if you're asking about a one-sided CI, we would obtain .
OK, in 2, my problem is figuring what is meant by +1, I would like to see ().
This could be +1 OR +1 OR .
IN any case you solve for .
IN 3, I'm guessing that you're asking for the lower value in a 2 sided interval