A certain restaurant offers 6 kinds of cheese and 2 kinds of fruit for its dessert platter. If each dessert platter contains an equal number of kinds of cheese and kinds of fruit, how many different dessert platters could the restaurant offer?
8
12
15
21
27
P(1C1F)+P(2C2F)=C(6,1)*C(2,1)+C(6,2)*C(2,2)=12+15=27
相同种类,最多两种
因为每个拼盘水果与奶酪的种类的数量是相同的(看懂题!!!),所以从大的方面就有两种情况:一种奶酪一种水果,两种奶酪两种水果。(因为水果最多只有两种哈)
(1)在水果里选一种C1 2,就有两种选择;在奶酪里选一种C1 6,就有六种选择,一共就是2*6=12种
(2)在水果里选两种C2 2,就有一种选择;在奶酪里选两种C2 6=6!/(2!*4!)=15,就有15中选择,一共就是1*15=15种
然后将上面两种情况相加,就是27中选择。
没有读懂题If each dessert platter contains an equal number of kinds of cheese and kinds of fruit,,这句话没看清意思
In case we serve 1 of each 6C1*2C1=6*2=12
In case we serve 2 of each 6C2*2C2=15*1=15
=> 15+12=27