how many ways can 4 baseball players and 4 basketball players be selected from 15 baseball players and 9 basketball players?
"C^{15}_4 \\times C^{9}_4 = \\frac{15!}{4!(15-4)!} \\times \\frac{9!}{4!(9-4)!} \\\\\n\n= \\frac{12 \\times 13 \\times 14 \\times 15 }{2 \\times 3 \\times 4} \\times \\frac{6 \\times 7 \\times 8 \\times 9}{2 \\times 3 \\times 4} \\\\\n\n= 1365 \\times 126 = 171990"
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