Question

plz help me users!!!!!!

Answer 1

Hola User_________________

Here is YOUR Answer...!!!
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↪⭐Actually welcome to the concept of the P AND C ....

↪Since tho property used is ....


↪nCp = nCr


↪then always p+ r = n

↪so applying we get as ...

↪r = 15

↪and after solving we get as ...,

↪⭐18C15 = 816
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↪⭐Hope it helps u...☺

Answer 2

Answer: 816

Step-by-step explanation:

Given,

$^{20}C_r=^{20}C_{r-10}\\\;\\We\;know\;that\\\;\\if,\;\;^nC_r=^nC_p\implies\;r+p=n\\\;\\Therefore,\\\;\\r+(r-10)=20\\\;\\2r=20+10\\\;\\2r=30\\\;\\r=15\\\;\\Now,\\\;\\^{18}C_r=^{18}C_{15}\\\;\\^{18}C_r=\frac{18!}{(18-15)!\times15!}\\\;\\^{18}C_r=\frac{18!}{(3!\times15!}\\\;\\^{18}C_r=\frac{18\times17\times16\times15!}{3!\times15!}\\\;\\^{18}C_r=\frac{18\times17\times16}{3!}\\\;\\^{18}C_r=\frac{18\times17\times16}{3\times2}\\\;\\^{18}C_r=816$

Note:  $^nC_r=\frac{n!}{(n-r)!\times\;r!}$