According to the Pew Research Center, in 2015, 19% of all American adults had Twitter accounts. Suppose this is true now. 

a. If a random sample of 500 Americans is taken, use the normal approximation to the binomial distribution to determine the probability that between 17% and 21% of the sample has a Twitter account. 

b. Do you think the percentage of all American adults with a Twitter account is now larger than 19% or smaller than 19%? How will this impact the probability you calculated in (a)?