Sampling Distribution of p

The distribution of the mean number of successes
The sampling distribution of $p$ is the distribution of the mean number of successes. It has a mean equal to the population proportion.
$.75$
The mean of the sampling distribution of $p$ is equal to the population proportion. It is $225/300 = .75$ .
$.137$
The standard error of $p = sqrt[p(1-p)/N] = sqrt[(.75)(.25)/10] = .137$