Answered

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You want to send postcards to 15 friends. In the shop there are only 3 kinds of postcards. In how many ways can you send the postcards, if

Sagot :

MrRoyal

Answer:

455 ways

Step-by-step explanation:

Given

[tex]n = 15[/tex] --- friends

[tex]r = 3[/tex] -- available postcard kinds

Required

Ways of sending the cards

The question is an illustration of combination and the formula is:

[tex]^nC_r = \frac{n!}{(n - r)!r!}[/tex]

So, we have:

[tex]^{15}C_3 = \frac{15!}{(15 - 3)!3!}[/tex]

[tex]^{15}C_3 = \frac{15!}{12!*3!}[/tex]

Expand

[tex]^{15}C_3 = \frac{15*14*13*12!}{12!*3*2*1}[/tex]

[tex]^{15}C_3 = \frac{15*14*13}{3*2*1}[/tex]

[tex]^{15}C_3 = \frac{2730}{6}[/tex]

[tex]^{15}C_3 = 455[/tex]

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