Consider the set of integers between 1 and 18, inclusive. How many unique numbers mustbe selected from this set to guarantee that at least one pair of these numbers has a sum of18?

Awoman has 14 different shirts: 10 white shirts and 4 red shirts. if she randomly chooses 2 shirts to take with her on vacation, then what is the probability that she will choose two white shirts? show your answer in fraction and percent, round to the nearest whole percent.