d = [10, 20, 3, 5, 30]: 5 parenthesizations

grouping                    cost
(A1(A2(A3A4)))              8250
(A1((A2A3)A4))              9300
((A1A2)(A3A4))              1950
((A1(A2A3))A4)              2800
(((A1A2)A3)A4)              2250

cheapest : ((A1A2)(A3A4)) at 1950
dearest  : (A1((A2A3)A4)) at 9300
ratio    : 4.77 times
