問數

lamin

A flock of 6birds is to be chosen from 10 blue and 5 yellow birds in a cage. Find the number of ways this flock may be chosen if

the flock must contain at least 3 blue birds and at least two yellow birds,
and two particualr blue birds cannot be placed together in the flock

ans10C3-8C1)X5C3+(10C4-8C2)X5C2
=2940
10C3-8C1 同10C4-8C2 係咩意思???

choy991044

因為要 at least 3 blue birds and at least two yellow birds,
所以 6 birds 既組合只有 [I]i)[/I] 3 blue +3 yellow or [I]ii)[/I] 4 blue + 2 yellow

i)  because two particualr blue birds cannot be placed together in the flock, 而只有 8C1會有機會做到 two particualr blue birds are placed together in the flock, 所以要減 8c1

ii) 個 8c2 同上

解得好差, 唔明再問啦  

lamin

[QUOTE=choy991044]因為要 at least 3 blue birds and at least two yellow birds,
所以 6 birds 既組合只有 [I]i)[/I] 3 blue +3 yellow or [I]ii)[/I] 4 blue + 2 yellow

i)  because two particualr blue birds cannot be placed together in the flock, 而只有 8C1會有機會做到 two particualr blue birds are placed together in the flock, 所以要減 8c1

ii) 個 8c2 同上

解得好差, 唔明再問啦  [/QUOTE]

我明la,thanks

CYBASTER

applied math來的?

CYBASTER

[QUOTE=choy991044]因為要 at least 3 blue birds and at least two yellow birds,
所以 6 birds 既組合只有 [I]i)[/I] 3 blue +3 yellow or [I]ii)[/I] 4 blue + 2 yellow

i)  because two particualr blue birds cannot be placed together in the flock, 而只有 8C1會有機會做到 two particualr blue birds are placed together in the flock, 所以要減 8c1

ii) 個 8c2 同上

解得好差, 唔明再問啦  [/QUOTE]8c1..同8c2..
清楚d講可以話係2c2 x 8c1同2c2 x 8c2

choy991044

[QUOTE=CYBASTER]applied math來的?[/QUOTE]
m&s

CYBASTER

[QUOTE=choy991044]m&s [/QUOTE]
applied math都有呢d~