The way to judge whether a number is closer to that number can be reduced by the number it is close to. The smaller the difference, the closer it is. Of course, this difference is positive.

For example, which number is closer, 7, 3 or 5? Then we can subtract these two numbers from 7. One difference is 4 and the other is 2, so 2 is less than 4, so 5 is closer.