Question

A certain spinner has equally sized slices. The probability of landing on a red slice is 4/9. What are the odds in favor of landing on a red slice?

Answer 1

There are 4 red slices out of 9 total. So there are 9-4 = 5 slices that are not red. The odds in favor of landing on red is 4:5

We basically write the number of ways to get what we want (4), followed by a colon, then the second number is the number of ways to get what we don't want (anything but red; 5 ways)

So that's why the answer is 4:5

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Side Note -- If we want the odds against, we simply flip the ratio. The odds against would be 5:4 because there are 5 ways to lose and 4 ways to win. This is assuming that landing on red means you win.