Average Weight

Let $a_1, a_2, \cdots ,a_8$ be the weights of the 8 dogs from the lightest to heaviest (in pounds).

For the maximum range, we assume that $a_1 = a_2 = \cdots = a_7 = 40$. Then $5\times 40 + a_8 = 6(55)$, $a_8 = 130$.

Maximum range = 90 pounds.