ONE SIMPLE MATH

(a) Unit price for 1 gram of A = 0.6 x 0.08 + 0.4 x 2.5 = 1.048
Unit price for 1 gram of B = 0.7 x 0.08 + 0. 3 x 2.5 = 0.806
% higher of A = (1.048 - 0.806)/0.806 x 100% = 30%
(b)
Original unit price of C = (1.048 x 5 + 0.806 x 3)/(5 + 3) = 0.95725
New price of A = 0.6 x 0.08(1 + 80%) + 0.4 x 2.5(1 - 25%) = 0.8364
New price of B = 0.7 x 0.08(1 + 80%) + 0.3 x 2.5(1 - 25%) = 0.6633
So new price of C = (0.8364 x 5 + 0.6633 x 3)/(5 + 3) = 0.77149
So % change in C = (0.77149 - 0.95725)/0.95725 x 100% = - 19.4%