As a general rule, the sampling distribution of the sample proportions can be approximated by a normal probability distribution whenever

a)np greater than or equal to 5
b) n(1-p) greater than or equal to 5
c) n greater than or equal to 30
d) both a and b are true
a continuous random variable is uniformly distributed between a and b. the probability density function between a and b is
a) zero.
b) (a - b).
c) (b - a).
d) 1/(b - a).

a population has a mean of 84 and a standard deviation of 12. a sample of 36 observations will be taken. the probability that the sample mean will be between 80.54 and 88.9 is

a) 0.0347.
b) 0.7200.
c) 0.9511.
d) none of the alternative answers is correct.