A construction firm deals with lots of invoices. 20% of the all the invoices show amounts greater than $800. Imagine that the firm chooses a random sample of 50 invoices.

1)What is the mean of the sample proportion of invoices with amounts in excess of $800?

2)What is the standard error of the sample proportion of invoices with amounts in excess of $800?

3)What is the probability that more than 22.7% of these 50 invoices are for more than $800?

4)What is the probability that at least 25% of these 50 invoices are for more than $800?