2.6.26. A group of n families. each with m mem bers, a.re to be lined up for a photograph. Tn h ow many ways can t he 11m people be arra nged if members of a family m ust stay together?
2.6.27. Suppm.e tha t ten people. i ncluding you and a friend, line up for a grou p pict ure. How many ways can the photographer rearrange the line if she wants to keep exactly three people between you and your friend?
2.6.2&. Theorem 2.6.l was t he first ma thematical result known to have been proved by ind uction, that feat being accomplished in 1321 by Levi ben Gerson. Assume that we do not k now the mulliplication rule. Prove t he theorem the way Levi hen Gerson did.
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