a bag contains 6 green balls and 7 white balls . if two balls are drawn simultaneously , what is the probability that both balls are the same colour ?
"the total number of ways to draw two balls is 13 c 2 = 78 the number of ways to draw two green balls is 6 c 2 = 15 the number of ways to draw two white balls is 7 c 2 = 21 p ( two balls of the same colour ) = 36 / 78 = 6 / 13 the answer is d ."
add(multiply(divide(7, add(6, 7)), divide(subtract(7, const_1), subtract(add(6, 7), const_1))), multiply(divide(subtract(6, const_1), subtract(add(6, 7), const_1)), divide(6, add(6, 7))))