The first assignment in a statistical computing class involves running a short program. If

past experience indicates that 40% of all students will make no programming errors, compare

the (approximate) probability that in class of 50 students

a. At least 50% will make no error

b. Between 30% and 50% will make no errors

Please show step by step and I will rate best answer!! Thank you!

for part (a), I know this is binomial with normal approximation? I know that I need to calculate the standard deviation first but I'm confused with the actual formula for that, is it sqrt((p(1-p))/n)?? Or just sqrt(p(1-p))? I know the mean is n*p. After getting the standard variance,

I calculate P(x>=0.5) ----> 1- pbinom(0.5,mean,standard deviation) right?