Answer:
The mean of the sampling distribution of p is of 0.7 and the standard deviation 0.029
Explanation:
We use the Central Limit Theorem to solve this question. So
Central Limit Theorem
For a proportion p in a sample of size n, the sampling distribution of the sample proportion will be approximately normal with mean
and standard deviation

Percentage of 70%, sample of 250.
This means that

Mean:

Standard deviation:

The mean of the sampling distribution of p is of 0.7 and the standard deviation 0.029