kaplan trick question

[resilient]

What is the percent profit of an ice cream seller makes on a vanilla ice cream if vanilla ice cream costs him 90 cents per scoop to make and he sells it at 1.20 cents per scoop.
a. 25%
b.30%
c.33.33%
d.40%
e.50%

elementary question and quite simple. BUT I chose 25% instead of 33.333%. I set the 30 cents profit as numerator and denominator of 120 cents. instead qa is 30 cent profit over 90 cent cost.


WHERE DID i GO WRONG AND WHAT IS WRONG WITH MY LOGIC?

please explain thanks alot and please do not explain the actual math, I am looking for the reason why I set the numerator wrong! thanks in advance

[aarunibens]

In such questions, you have to be sure of the 'Denominator' and that should always be according to the question. If it isn't specified in the question, you should always take the original cost.

Here the Cost Price is 90 cents. The Selling price is 120 cents. Since it is not specified in the question whether the ice cream seller's profit is to be calculated on Cost Price or Selling Price, we estimate it on the Cost Price.

And hence the numerator becomes the difference of SP - CP and denominator becomes CP

So, 30 / 90 * 100 = 33.33%

[Stuart@KaplanGMAT]

Not sure why the title of this post says "trick question" - this is a very basic (and common) percent change question.

Percent change = amount of change / original amount = (new - original) / original.

In this case, the original price is 90 cents and the new price is 120.

Plugging in:

(120 - 90) / 90 = 30/90 = 1/3 = 33.3%

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Also ..Profit and loss are always calculated on the Cost price of the article.