20 balls are numbered 1 to 20 . a ball is drawn and then another ball is drawn without replacement . what is the probability that both balls have even numbers ?
"p ( 1 st ball is even ) = 10 / 20 p ( 2 nd ball is also even ) = 9 / 19 p ( both balls are even ) = 10 / 20 * 9 / 19 = 9 / 38 the answer is c ."
multiply(divide(add(const_4, const_4), 20), divide(subtract(add(const_4, const_4), 1), subtract(20, 1)))