when a random experiment is conducted , the probability that event a occurs is 1 / 3 . if the random experiment is conducted 4 independent times , what is the probability that event a occurs exactly twice ?
"one case is : 1 / 3 * 1 / 3 * 2 / 3 * 2 / 3 = 4 / 81 the total number of possible cases is 4 c 2 = 6 p ( event a occurs exactly twice ) = 6 * ( 4 / 81 ) = 8 / 27 the answer is a ."
subtract(1, divide(const_2, 3))