The intent of the problem seems to be as follows:
Because of a clerical error, a shirt was marked with a selling price that was x% less than the cost price of the shirt. After the error was discovered, the selling price of the shirt was doubled, with the result that the corrected selling price was x% greater than the cost price of the shirt. What is the value of x?
12.5 %
25%
33 1/3%
40%
50%
We can PLUG IN THE ANSWERS, which represent the value of x.
When the correct answer choice is plugged in, the corrected selling price will be DOUBLE the incorrect selling price.
Let the cost price = 100.
Answer choice D: 40%
Incorrect selling price = 100 - (40% of 100) = 60.
Corrected selling price = 100 + (40% of 100) = 140.
Here, the corrected selling price (140) is MORE THAN DOUBLE the incorrect selling price (60).
Eliminate D.
Answer choice B: 25%
Incorrect selling price = 100 - (25% of 100) = 75.
Corrected selling price = 100 + (25% of 100) = 125.
Here, the corrected selling price (125) is LESS THAN DOUBLE the incorrect selling price (75).
Eliminate B.
Since 40% yields a corrected selling price that is MORE than double the incorrect selling price, and 25% yields a corrected selling price that is LESS than double the incorrect selling price, the required percentage must be BETWEEN 25% and 40%.
The correct answer is
C.
Answer choice
C: 33 1/3%
Since 33 1/3% = 1/3, let the cost price = $30.
Incorrect selling price = 30 - (1/3 of 30) = 20.
Corrected selling price = 30 + (1/3 of 30) = 40.
Success!
The corrected selling price (40) is double the incorrect selling price (20).
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