According to a recent survey, 71% of teens age 12-17 in a certain country used social networks in 2009. A random sample of 140 teenagers from this age group was selected. a) calculate the standard...

According to a recent survey, 71% of teens age 12-17 in a certain country used social networks in 2009. A random sample of 140 teenagers from this age group was selected.

a) calculate the standard error of the proportion.

b) what is the probability that less than 73% of the teens from this sample used social networks?

c) what is the probability that between 70-80% of the teens from this sample used social networks?

Please help! I am struggling. Thank you!