The odds of spinning red on a spinner are 2:7. What is the probability of not spinning red?

5:7.

To figure this, you just need to read it like the probability of getting a red is 2/7, and therefore any other color on the spinner must be NOT red. You consider the complement, which here would be:

1 - P (landing on red) = 1 - 2/7 = 5/7

In general, the complement of a single event is 1 minus the probability of that event occuring.