suppose a true approval rating of a particular candidate in the population is 48%

If a simple random sample of 3000 people is done, what is the probability that the resulting percent that approve of the person is above 50%?

Question

suppose a true approval rating of a particular candidate in the population is 48%

If a simple random sample of 3000 people is done, what is the probability that the resulting percent that approve of the person is above 50%?

hyroko · Answer

@kropot72 care to help me with one more?

kropot72 · Answer

@Hyroko This can be solved by using the normal approximation to the binomial distribution.

dumbcow · Answer

http://stattrek.com/hypothesis-test/proportion.aspx?Tutorial=AP

hyroko · Answer

I'm sorry I don't understand either of those suggestions.

hyroko · Answer

Can someone actually help me figure this out?

hyroko · Answer

How do I calculate this without knowing the standard deviation?

dumbcow · Answer

you can calculate the std dev
$$\sigma = \sqrt{\frac{P(1-P)}{n}} = \sqrt{\frac{.48(.52)}{3000}}$$
find z-score
$$z = \frac{p-P}{\sigma} = \frac{.5-.48}{\sigma}$$
Use normal table to find 
$$P(Z >z) = 1-P(Z < z)$$
The table will give probability of less than given z-value