Hi, can someone help me solve this profit question from GMAT Quant section?

Question

On a certain day, a bakery produced a batch of rolls at a total production cost of $300. On that day, of the rolls in the batch were sold, each at a price that was 50 percent greater than the average (arithmetic mean) production cost per roll. The remaining rolls in the batch were sold the next day, each at a price that was 20 percent less than the price of the day before. What was the bakery’s profit on this batch of rolls? 
A. $150
 B. $144 
C. $132 
D. $108 
E. $90

B.K Sharma · Accepted Answer

This one looks messy but actually follows a standard GMAT profit structure. Let the number of rolls be n and the cost per roll be p, so total cost is np = 300.
Now, on Day 1, 4/5 of the rolls were sold at 1.5&times; the production cost (50% higher). So revenue from Day 1 is: (4/5)n &times; (1.5p) = (6/5)*np
The remaining 1/5 of the rolls were sold at 20% less than the selling price from Day 1 &mdash; that&rsquo;s 0.8 &times; (1.5p) = 1.2p. So Day 2 revenue = (1/5)n &times; 1.2p = (6/25)*np
Total revenue = (6/5 + 6/25)*np = (36/25)*np Profit = (36/25)*np &minus; np = (11/25)*np = (11/25) &times; 300 = $132
Correct answer: C

S Raghav · Answer

The key is translating the info into clean math. Start by treating total cost as 300 = n &times; p.
&bull; Day 1: 4/5 of rolls sold at 50% more than cost &rarr; selling price = 1.5p Revenue = (4/5)*n &times; 1.5p = (6/5)*np &bull; Day 2: 1/5 rolls left, sold at 20% less than 1.5p &rarr; new price = 1.2p Revenue = (1/5)*n &times; 1.2p = (6/25)*np &bull; Total revenue = (6/5 + 6/25)*np = (36/25)*np &bull; Profit = revenue &minus; cost = (36/25)*np &minus; np = (11/25)*np = (11/25)*300 = 132
It&rsquo;s a profit question wrapped in a word problem. Correct pick: C.