Hi, quick stat question. So I have had a few statistics questions which involve

Question

Hi, quick stat question.

So I have had a few statistics questions which involve proportions. Some have given a proportion and the sample size then ask the probability of a number of something happening (eg number of people who voted instead of the proportion who voted). Others give me a probability and sample size and ask the probability of a proportion.

I know well the general process for these problems. However, I am confused when I should be using the standard deviation formula sqrt(np(1-p)) or sqrt((p(1-p)/(n))?

I know the first is for binomial distributions, but aren't most probabilities binomial? (eg. .2 probability you live in china vs .8 you dont)?

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Result:

I know well the general process for these problems. However, I am confused when I should be using the standard deviation formula sqrt(np(1-p)) or sqrt((p(1-p)/(n))?

I know the first is for binomial distributions, but aren't most probabilities binomial? (eg. .2 probability you live in china vs .8 you dont)?

When the question is about x, use sqrt(np(1-p))

Example: What is the probability of obtaining 45 or fewer heads in 100 tosses of a coin?

When the question is about p, use sqrt((p(1-p)/(n))

Example:

Based on 120 customers are surveyed 73 percent are very satisfied. Based on whether we can claim at least 80 percent of the company's customers are very satisfied.

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