Maths-
General
Easy
Question
A person writes letters to 6 friends and addresses the corresponding envelopes. In how many ways can the letters be placed in the envelopes so that at least 4 of them are in wrong envelopes ?
- 72
- 719
- 664
- 135
The correct answer is: 664
No. of ways = 6C2 . 4!
+ 6C15! 
+ 6C0 . 6! 
= 135 + 264 + 265 = 664
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