TextBook Question. Don't understand how to complete it? With what formula, what steps?

According to an Australian Government report, retail trade is the second largest employing industry in Australia with more than 1.2 million workers, or 10.5% of working Australians The report shows that the percentage of those employed in retail trade in November 2012 who were working part-time was 50%. Assuming this percentage is still current:

1. If you select a random sample of 400 Australian retail trade workers, what is the probability that the sample has between 45% and 50% who are employed part-time?

2. If a current sample of 400 Australian retail trade workers has 51.2% who are employed part-time, what can you infer about the population estimate of 50%? Explain.

3. If a current sample of 100 Australian retail trade workers has 51.2% who are employed part-time, what can you infer about the population estimate of 50%? Explain.

4. Explain the difference in the results in (2) and (3).