Question 634329
The only trick to this is figuring out how to set up the price matrix so that a) It can be multiplied with the 3x3 matrix of stores and items sold; and b) that the multiplication will multiply the right numbers together.<br>
To multiply with the 3x3 matrix we will either use a 1x3 matrix on the left or a 3x1 matrix on the right. If we try a 1x3 matrix on the left of the 3x3, we end up multiplying a row of prices with a column of all the same device. (Try it out and see.) Multiplying with a 3x1 matrix on the right gets the right kinds of numbers multiplied: number of a device times the price of the device. So that is the way to go:
{{{(matrix(3, 3, 50, 75, 80, 45, 79, 63, 58, 67, 98)) * (matrix(3, 1, 240, 199, 99)) = (matrix(3, 1, 50*240+75*199+80*99, 45*240+79*199+63*99, 58*240+67*199+98*99)) = (matrix(3, 1, 34845, 32758, 36955))}}}
So CircuitCity's revenue: $34845
Bestbuy's revenue: $32758
Target's revenue: $36955