Hi there,
I'm fairly new to R and I need some help with my R code to for the below question. I've managed to calculate the z using pnorm(0.05).

Question:
Let X ~ N (100, 202). Find two values, a and b, symmetric about the mean, such that the probability of the random variable taking a value between them is 0.99

Without solving the question completely, what I can suggest is that use the information about symmetry of a and b with respect to mean to reduce the problem to find just one unknown, say c, and then find the value of c theoretically as a function of a quantile of the standard normal distribution, and then use the qnorm function in R to calculate the value.