Thread: normal distribution:

An audit of an area agricultural office revealed 120 out of 500 randomly chosen records relating to smallholdings in the region to be inaccurate in some minor detail. Using this as an indication of the overall proportion of incorrect records in the office, what is the probability that a research worker using another 100 of these records in a survey will find that less than 15 of them contain any error?

Originally Posted by Louisa88

An audit of an area agricultural office revealed 120 out of 500 randomly chosen records relating to smallholdings in the region to be inaccurate in some minor detail. Using this as an indication of the overall proportion of incorrect records in the office, what is the probability that a research worker using another 100 of these records in a survey will find that less than 15 of them contain any error?

X ~ Binomial(n = 100, p = 120/500 = 6/25).

Judging from your title, you're probably expected to use the normal approximation to calculate Pr(X < 15). Where are you stuck?

Thanks