Hi,
This is a Algebra question,
There are two ways to solve most of the Algebra question in GMAT.
1. Normal equation way.
2. Plugging in/ Back-Solving.
1. Normal Equation way:
This is like your school math; assume variables for the unknown quantities in the question.
Also try to keep variables minimal.
Here in this question,
Let “x” the usual price of each calendar and “n” be the usual number of purchase,
Question says, 20 percent discount given on the usual price and 50 percent more number of calendars purchased.
Price No. of Items“x” “n"
0.8x 1.5n
From the question,
120 * x = (0.8x)*(1.5n)
So n = 100
So that’s it, you just need to form the equation and find a relation given in the question.
In 30 seconds, if you are not able to construct the equation then think about the alternate way.
2. BackSolving:
Whenever it’s a equation type question, we can also use the answer choices and work backwards rather than solving it using equations.
Always start with answer choice “C”, because answer choices will be in order in GMAT.
Here the answer choice C is 100.
That is it means to usually hundred calendars purchased,
Let’s check whether it matches condition given in the question,
Price No. of Items“x” 100
0.8x 150
Question says,
120 * x = 150 * 0.8x
Yes it is, 150 * 0.8 = 120.
Answer choice “C” matches the condition that, 120 times the initial cost is equal to the total cost.
So the answer is C.
Hope this helps
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