If the probability of something happening is x, then the probability of it not happening is 1 - x.
If the probability that it will rain is 3/8, then the probability that it will not rain is 1 - 3/8 = 5/8
The probability of the spinner landing on yellow is 3/8.
The probability of the spinner not landing on yellow is 1 - 3/8 = 5/8
Let's have a go at some questions now.
If the probability of you getting all the questions correct is 9/10, what's the probability that you don't get them all correct?
Could it be 1 - 9/10, which is 1/10?!