After taking 40 observations you construct a 90 con dence in

After taking 40 observations, you construct a 90% con dence interval for . You are told that your interval is 3 times too wide (i.e., your interval is 3 times wider than what was required). Your sample size should have been

a) 120

b) 810

c) 360

d) 9

SHOW YOUR WORK.

Solution

width of confidence interval= z(0.95)*sd/sqrt(n)

as confidence interval is 3 times wider for 40 observations

then for required width n = 40*3^2 = 360

c) 360 is answer