A seven sided number cube with sides numbered 1,2,3,4,5,6,7 is rolled. What is the probability that an odd number or a seven is rolled

List out the odd numbers: {1, 3, 5, 7}

List out the values that are 7, which is just the set { 7 }

Combine the two sets {1, 3, 5, 7} and { 7 } to get {1, 3, 5, 7}. No change happens with the first set because of the overlap.

There are 4 items in the set {1,3, 5, 7} out of 7 items total {1,2, 3, 4, 5, 6, 7}

So the probability expressed as a fraction is 4/7

This is roughly approximate to 0.5714 (which is roughly 57.14%)