# Browsing category statistics 1

## Ask Uncle Colin: why does the normal distribution stop at $z=\pm 4$?

Dear Uncle Colin, In Statistics, we were shown a picture of the standardised normal distribution curve, and the base stops at +4 and -4. Why is it not $\pm 5$, $\pm 10$, or anything else? Is there something special about 4? -- Got An Unanswered Statistics Struggle Dear GAUSS, The

## Conditional probability and the normal distribution

Until fairly recently, you could throw a handkerchief over the variety of normal distribution questions you might expect to see in an EdExcel S1 exam. It would be one or more of: given a mean and a standard deviation, work out the probability that the random variable is larger or

## How do I decide whether to take things away from 1 (Normal distribution)

A student asks: I'm never sure whether I have to take the number that comes out of the normal distribution table away from 1. How do you know? It's a familiar song: you've worked out your $z$-score (naturally, you remember that this means "how many standard deviations you are above