Hi, in this question:

-A bank has determined that the monthly balances of the saving accounts of its customers are normally distributed with an average balance of $1,200 and standard deviation of 250. If a sample of 36 customers is selected, a. What is the probability that the average monthly balances are between $1,255 and $1,275? b. What is the probability that the total balance of the saving accounts for the 36 customers is less than $41,000?-

Why is the answer to B: -b. If total is $41000 ,then = 0.5 0.4292 = 0.0708-