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The answer would be C) because there are 11 possibilities of who can line up first, and after the first person, 10 possibilities, then 9, and so on. So you would need to multiply 11x10x9x8x...x1.
This is simple , minus 50 from 100 and that gives you 50 left . then divide that by 2 and that gives you 25 . so the minimum number of sales required is 25 . hope this helps :)<span />