Let's denote the total number of cookies baked as N and the cost per cookie as C.
Initial Price
The initial selling price per cookie was set at 20% higher than the cost:
P1=C×1.20
Selling at the Initial Price
The shop sold 3/5 of the cookies at the initial price:
Cookies sold= 3/5 N
Revenue from these cookies=3/5 N×P1= 3/5 N×1.20C= 3/5 ×1.20CN=0.72CN
Remaining CookiesAfter selling 3/5 of the cookies, the remaining cookies were:
N remaining =N− 3/5 N= 2/5 N
Increased Price
By noon, the shop increased the price by an additional 25%:
P2 = P1×1.25=1.20C×1.25=1.50C
Selling at the Increased PriceThe shop sold half of the remaining cookies at the increased price:
Cookies sold= 1/2 × 2/5 N= 1/5 N
Revenue from these cookies= 1/5 N×P2 = 1/5 N×1.50C=0.30CN
Remaining CookiesAfter selling half of the remaining cookies, the remaining cookies were:
N remaining = 2/5N− 1/5 N= 1/5 N
Reduced PriceIn the evening, the shop reduced the price by 20% to clear out the rest:
P3=P2×0.80=1.50C×0.80=1.20C
Selling at the Reduced Price
The shop sold 3/4 of the remaining cookies at the reduced price:
Cookies sold= 3/4 * 1/5 N
Revenue from these cookies=3/20𝑁×𝑃3
Revenue from these cookies=3/20 N×1.20C=0.18CN
Total RevenueThe total revenue from all sales is the sum of the revenues from each phase:
Total Revenue=0.72CN+0.30CN+0.18CN=1.20CN
Total CostThe total cost of the batch of cookies is:Total Cost=N×C=CN
Gross ProfitThe gross profit is the total revenue minus the total cost:
Gross Profit=Total Revenue−Total Cost=1.20CN−CN=0.20CN
Gross Profit as a Percentage of Total Cost
The gross profit as a percentage of the total cost is:(0.20𝐶𝑁)/𝐶𝑁×100%=20%
0.20 ×100%=20%
Therefore, the coffee shop's gross profit from the sale of the cookies as a percentage of its total cost for the batch is:20%