負の数（マイナスの数）のはじめ

On a number line, the positive numbers ($1,2,3,\dots$) sit to the right of $0$, and the negative numbers ($-1,-2,-3,\dots$) sit to the left. The further right you go, the bigger the number; the further left, the smaller. Picturing the number line makes negative numbers much easier to understand.

On the number line, numbers further to the left are smaller. So $-7$ is less than $-2$ (we write $-7<-2$), and $0$ is greater than any negative number. With temperature, $-5$°C is colder than $-1$°C. Below sea level, a 'more negative' number means deeper. Watch out: a number can look big with its digits but still be small because it is negative.

Think of adding as moving right along the number line, and subtracting as moving left. For example, $-3+5$ means start at $-3$ and move $5$ to the right, landing on $2$. The other way, $4-7$ means start at $4$ and move $7$ to the left, passing through $0$ down to $-3$. Practising by stepping along the line with your finger makes it click quickly.