For some reason, I can’t seem to get this. I’ve used normalpdf and it comes up as a number that doesn’t make sense. The exact question is as follows:
The tread life of a particular brand of tire is a random variable best described by a normal distribution with a mean of 90,000 miles and a standard deviation of 6,000 miles. If we select a tire of this brand at random, what is the probability that the tire treat is worn out before 81,000 miles?
TLDR; Mean: 90,000 SD: 6,000 X: 81,000
Obviously change numbers up if you’d like, just looking for a good explanation of how to solve this sort of problem using a TI83.