Revenue = Price x Quantity.
Before I get into my solution, let me take an example:
Let's say the factory doubles the price.
And after doubling the price, the revenue remains the same.
What would have happened to the Quantity?
If the price doubles, but the revenue remains the same, the quantity must be halved.
Since the overall revenue was the same, the increase in the price will correspond to a proportional decrease in the quantity. In maths terms, if the price became 2x, the quantity would have become 1/2x.
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We can answer the question using this underlying understanding.
1. "the factory
raised the price of each widget
to X% of the original price"
a. The price has been raised.
b. The price is not raised
by X%. It is raised
to X% of the original price. e.g. Say last month's price was $100, and this month's price is $110. Is X = 110 or 10? The price has been raised
by 10%. It has been raised
to 110% of the previous price. So, X = 110.
Since the price has been raised,
X > 100.
2. "the factory only sold Y% as many widgets as last month, and the total revenue from the sale of widgets was equal for last month and this month."
a. The factory sold Y% as many widgets, not Y% less than last month, but Y%.
e.g. Let's say the quantity sold went down from 100 to 80. Would Y be 20 or 80? The factory sold 80%
as many widgets as last month. Or, the factory sold 20%
less widgets than last month. In this example, Y would be 80.
b. The total revenue was equal. The price per widget had increased. So, the quantity of widgets must have reduced.
Y < 100.
X can only be 150, 160, or 180.
Y can only be 50, 62.5, or 75.
Now, how to deal with the remaining values.
I will start with the potential answers for X: 150, 160, 180 and check if the corresponding value of Y is there in the table. (We could start with Y as well and then check if the corresponding value of X exists in the table. I chose X because I want to avoid dealing with 62.5/100.)
i.
If the price became 150%, = 150/100 = 3/2 times, the quantity would have to be 2/3 times last month's quantity to keep the revenue the same.
2/3 times last month's quantity means 66.7% of the old quantity. (Knowing 1/3 = 33.3% helped me here.)
66.7% is not an option. I'll reject 150 for X.
ii.
If the price became 160% = 160/100 = 8/5 times, the quantity would have to be 5/8 times last month's quantity to keep the revenue the same.
5/8 times last month's quantity means 62.5% of the old quantity. (I used a calculator to calculate 5/8).
62.5 is present in the table.
We could very well mark
X: 160
Y: 62.5
at this point and move on. We can't have two sets of values that would be consistent with the information provided. We've found one set of values that's consistent. This will be the only consistent pair.
iii.
Nevertheless, for practice, let me try X = 180.
If the price became 180% = 180/100 = 9/5 times, the quantity would have to be 5/9 times last month's quantity to keep the revenue the same.
5/9 times last month's quantity means 55.5% of the old quantity. (I knew that 1/9 = 11.11%. So, 5/9 must be 55.55%).
55.5 is not present in the table. Reject 180 for X.