Explanation:
To show that the system is uneconomical if four deliveries are made in a day, we need to find the profit (Y) for x machines and 4 deliveries:
Y = 12x - 2a - a (for 4 deliveries)
Y = 12x - 3a
We know that processing all deliveries must be done in a single day, so we have:
a = 4x
Substituting this into the profit formula, we get:
Y = 12x - 3(4x)
Y = 0
This means that the profit (Y) is zero when four deliveries are made in a day, making the system uneconomical.
To find the number of machines that would be used in order for profit to be maximized for four deliveries in a day, we need to differentiate the profit formula with respect to x and set it equal to zero to find the maximum:
dY/dx = 12 - 6a = 0 (for a = 4x)
Solving for x, we get:
12 - 6(4x) = 0
12 - 24x = 0
x = 1/2
Therefore, the maximum profit would be obtained by using 1/2 of a machine (which is not physically possible, so we would round up to one machine) for processing four deliveries in a day.