Needed assistance solving the following problem Thank you At

Needed assistance solving the following problem. Thank you,

At an online store, 74% customers pay with a credit card. Of the next 83 customers who make a purchase at this store, What is the probability that Pay with a credit card. what is the probability that at most 40 people pay with a credit card? how many of the 83 customers do you expect to pay with a credit card? what is the probability that the number of customers who pay with a credit card is within one standard deviation of the expected number?

Solution

Normal Distribution = Z= X- u / sd ~ N(0,1)                  

a)
P(X > 70) = (70-61.42)/3.9961
= 8.58/3.9961 = 2.1471
= P ( Z >2.147) From Standard Normal Table
= 0.0159                  
b)
P(X > 40) = (40-61.42)/3.9961
= -21.42/3.9961 = -5.3602
= P ( Z >-5.36) From Standard Normal Table
= 1                   P(X < 40) = (40-61.42)/3.9961
c)
Mean ( np ) =61.42