In a certain packet, there are ten balls of different weight. The weights are denoted by a, b, c, d, e, f, g, h, i, j where 'a' is the lightest ball and the 'j' the heaviest. The average weight of these ten balls is 30. If weight of the lightest ball is not counted, average weight of the remaining 9 balls will be p; and if weight of the heaviest ball is not counted, average weight of the remaining 9 balls will be q. If the sum of p and q is given as 20, what is the average weight of the lightest and the heaviest balls?