13 different biology books and 8 different chemistry books lie on a shelf . in how many ways can a student pick 2 books of each type ?
"no . of ways of picking 2 biology books ( from 13 books ) = 13 c 2 = ( 13 * 12 ) / 2 = 78 no . of ways of picking 2 chemistry books ( from 8 books ) = 8 c 2 = ( 8 * 7 ) / 2 = 28 total ways of picking 2 books of each type = 78 * 28 = 2184 ( option e )"
multiply(divide(divide(factorial(13), factorial(subtract(13, 2))), 2), divide(divide(factorial(8), factorial(subtract(8, 2))), 2))