How many ways can 5 boys and 5 girls be seated at a round table if: a. no restrictions are imposed b. the girls and boys are to occupy alternate seats c. 3 particulars girls must sit together d. 3 particulars girls must not sit together e. all the girls must sit together Solution: a. The number of arrangements of 10 persons to be seated at a round table is (n-1)! = (10-1)! = 9! = 362,880 b. __________________________________________________________________ _____________________________________________________________________ _____________________________________________________________________ ____________________ c. Consider the 3 particular girls as 1 group or unit. Since there are 2 girls and 5 boys to be seated, there area total of:5 seats for boys + 2 seats for girls + 1 group seat = 8seats (n) to be arranged in a circle . Thus, (n-1)! = (8-1)! = 7! = 5, 040 Moreover, the 3 girls can be arranged within its group in (3) (2) (1) = 6ways. By FPC, the required number of ways the 10 persos can be seated is 5, 040 x 6 = 30,240 d. . ____________________________________________________________________ ____________________________________________________________________ _____________________________________________________________________
Permutations and Combinations
If there are 5 dishes, they can be relished in any order at a time. In permutation, it should be in a particular order. In combination, the order does not matter. Take 3 letters a, b, and c. The possible ways of pairing any two letters are ab, bc, ac, ba, cb and ca. It is in a particular order. So, this can be called the permutation of a, b, and c. But if the order does not matter then ab is the same as ba. Similarly, bc is the same as cb and ac is the same as ca. Here the list has ab, bc, and ac alone. This can be called the combination of a, b, and c.
Counting Theory
The fundamental counting principle is a rule that is used to count the total number of possible outcomes in a given situation.
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