1.

There are 7 greeting cards,each of a different colour and 7 envelopes of same 7 colours as that of the cards .The number of ways in which the cards can be put in envelopes,so that exactly 4 of the cards go into envelopes of respective colour ,is

Answer»

`""^(7)C_(3)`
`2.""^(7)C_(3)`
`3!""^(4)C_(4)`
`3!""^(7)C_(3)""^(4)C_(3)`

Answer :B


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