permulation
2011-12-27 9:12 pm
there are 6 phones from Brand A and 5 phones from Brand B. If they are placed in one row, find the number of permutations if any two mobile phones from Brand B must not be placed next to each other.
回答 (1)
2011-12-27 9:30 pm
✔ 最佳答案
Solution: Place 6 mobile phones from Brand A first. There are 6!=720 permutations. Then inserts 5 mobiles phones from Brand B into 7 possible "holes"
* A1 * A2 * A3 * A4 * A5 * A6 *
There are 7P5 = 2520 permutations.
Total 720 * 2520 = 1814400 permutations.
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