4 A bag contains six identical balls numbered 2, 3, 4, 5, 6 and 7. (a) A ball is taken from the bag at random. Find, as a fraction in its lowest terms, the probability that the number on the ball is (i) a multiple of 3, (ii) prime. (b) All six balls are replaced in the bag. Two balls are taken from the bag, one after the other, without replacement. The numbers on the two balls are added together. (i) Complete this possibility diagram to show all the outcomes. (ii) Find the probability that the sum of the numbers is (a) odd, (b) less than 8.