Please help, I'm not sure what formulas to use.

A large national study finds that 10% of pregnant women deliver prematurely. A local obstetrician is seeing 20 pregnant women in the next week at their clinic.(round answers to 3 decimal places)

1. What is the probability that none will deliver prematurely?
2. What is the probability that fewer than 3 will deliver prematurely?
3. What is the probability that none will deliver prematurely if, in fact, the true percentage who deliver prematurely is 6%?
4. If the true percentage is 10% and this obstetrician has 125 pregnant women currently at their practice, how many would be expected to deliver prematurely? Remember this is number of people so answer appropriately.
5. What would the standard deviation be in number of women for that expected number of premature deliveries calculated in (d). Remember this is number of people so answer appropriately.