Permutation & Combination
2012-09-21 3:14 am
There are four $10- coins, three $5- coins, one $2 - coins and two $1 - coins. Find the no. of ways of choosing 3 coins from these 10 coins.
回答 (1)
2012-09-21 7:53 am
✔ 最佳答案
3 coins are difference :4C3 = 4 ways.2 coins are the same (3 possible cases : two $10 , two $5 or two $1)
and 1 other coin :
3C1 * (4-1)C1 = 3 * (4-1) = 9 ways.3 coins are the same (three $10 or three $5) :
2C1 = 2 ways.Total 4 + 9 + 2 = 15 ways.
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