The standard normal curve shown here is a probability density curve for a continuous random variable. this means that the area underneath the enitre curve is 1. what is the area of the shaded region between the two z-scores indicated in the diagram ? z=-1.21 z=0-84
a. 0.1131
b.0.6864
c.0.6844
d.0.1151
e.0.7995

Arandom sample of n = 25 observations is taken from a n(µ, σ ) population. a 95% confidence interval for µ was calculated to be (42.16, 57.84). the researcher feels that this interval is too wide. you want to reduce the interval to a width at most 12 units. a) for a confidence level of 95%, calculate the smallest sample size needed. b) for a sample size fixed at n = 25, calculate the largest confidence level 100(1 − α)% needed.