Six people, call them A, B, C, D, E, and F, are randomly divided into three groups of two. Find the probability that A and B are in the same group, as are C and D. (Do not impose unwanted ordering among groups.)
First lets find the number of permutations of three ordered groups, A and B, C and D and E and F: 3P3 = 6 However when the order in each of the pairs can be reversed, the number of arrangements meeting the required grouping becomes: 6 * 8 = 48. The total number of permutations of the 6 people is given by: 6P6 = 720. Therefore the required probability is found from: [tex] \frac{48}{720} = \frac{1}{15} [/tex]