A math problem! ! ! Use the law of large numbers and the central limit theorem to solve it.
Looking for the central limit theorem of p (x 1+x2+...x300 > =400)
[x1+x2+... x300-300 * (1.29)]/sqrt (300 * (0.423)) is approximate to the standard normal distribution, where 0.423 is the variance of x and1.29 is the mean of x.
So the demand = p ([x1+x2+.. x300-300 * (1.29)]/sqrt (300 * (0.423)) > =1.154) ≈.