in how many ways can i write letters to three out of 9 friends if i have exactly one post card,one inland letter and one envelope?
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Answer:
504
Step-by-step explanation:
Selecting 3 out of 9 friends, thus--->
9c3 = 9! / (9-3)! x 3!
But arranging also matters, thus multiply by 3!
9! / (9-3)! x 3! x 3!
= 9! / 6! [Cancelling out 3!]
= 9 x 8 x 7
= 504 ways!
Hope you understand!
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