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Nov 2011 p61 q6
2795
(i) 4 astronauts are chosen from a certain number of candidates. If order of choosing is not taken into account, the number of ways the astronauts can be chosen is 3876. How many ways are there if order of choosing is taken into account?
(ii) 4 astronauts are chosen to go on a mission. Each of these astronauts can take 3 personal possessions with him. How many different ways can these 12 possessions be arranged in a row if each astronaut’s possessions are kept together?
Solution
(i) When the order of choosing is taken into account, we need to multiply the number of combinations by the number of permutations of the 4 astronauts. The number of permutations of 4 astronauts is given by:
\(4! = 4 \times 3 \times 2 \times 1 = 24\)
Thus, the total number of ways is:
\(3876 \times 24 = 93024\)
(ii) Each astronaut has 3 possessions, and these possessions are kept together. We treat each astronaut's possessions as a single unit, so we have 4 units to arrange. The number of ways to arrange these 4 units is:
\(4! = 24\)
Within each unit, the 3 possessions can be arranged in:
\(3! = 6\) ways
Therefore, the total number of ways to arrange the possessions is: