Variance and the Standard Deviation

In San Francisco, 30% of workers take public transportation daily.
a) In a sample of 10 workers, what is the probability that exactly three workers take the public transport daily? [Hint: It is a Binomial Distribution Problem.]

f(3) =

b) In a sample of 10 workers, what is the probability that at least three workers take the public transport daily?

P(x?3)=1-f(0)- f(1)- f(2)
f(0) =
f(1) =
f(2) =
P(x?3)=1-f(0)- f(1)- f(2) =

c) How many workers are expected to take the public transportation daily?

E(X) =

d) Compute the variance and the standard deviation of the number of workers that will take the public transport daily.

Var(X) =
Standard Deviation =