Kombinatorika Dan Peluang > Dilarang Spam, jawaban berupa salinan, dll 2 soal Good Luck!

[tex] 11.\frac{28!}{(2r)!(28-2r)!} = 225.\frac{24!}{(2r-4)!(28-2r)!} \\ 11.\frac{28.27.26.25}{(2r)!} = 225.\frac{1}{(2r-4)!} \\ \frac{28.27.26.25.11}{(2r)(2r-1)(2r-2)(2r-3)} = 225 \\ 28.3.26.11 = (2r)(2r-1)(2r-2)(2r-3) \\ 14.13.12.11 = (2r)(2r-1)(2r-2)(2r-3) \\ 2r = 14 \\ r = 7 [/tex]

[tex] \frac{k!(7-k)!}{7!} - \frac{k!(8-k)!}{8!} = \frac{9}{5}.\frac{k!(9-k)!}{9!} \\ 1 - \frac{8-k}{8} = \frac{9}{5}.\frac{(9-k)(8-k)}{9} \\ \frac{k}{8} = \frac{(9-k)(8-k)}{8.5} \\ 0 = k^2 - 22k + 72 \\ k = 4 atau k = 18 [/tex]
Yang memenuhi adalah k = 4 karena (7-k), (8-k), dan (9-k) harus positif.