Yes, you're absolutely right. Thanks for correcting us!
Why, in answer c, is the z-score formula z=(50000-40000)/4000? Because the mean is 47000, should it be z=(50000-47000)/4000?
Normal distribution with given mean and variance is considered for solving the problem. For example, take a look https://en.wikipedia.org/wiki/Standard_normal_table
The standard normal distribution table provides the probability that random variable x is less than or equal to z. It does this for positive values of z only. So from given table we can find values of& P(x).
So values of p(x) are taken from the table of such kind.
how do you know P (x>50,000) = .62%? I am very confused when it comes to the P (X) part