A Store Currently Charges The Same Price for Each Towel That It Sells. GMAT Problem Solving

Question: A store currently charges the same price for each towel that it sells. If the current price of each towel were to be increased by $1, 10 fewer of the towels could be bought for $120, excluding sales tax. What is the current price of each towel?

(A) $ 1
(B) $ 2
(C) $ 3
(D) $ 4
(E) $12

“A store currently charges the same price for each towel that it sells.”- is a topic of the GMAT Quantitative reasoning section of GMAT. This question has been taken from the book “The Official Guide for GMAT Review”. To solve GMAT Problem Solving questions a student must have knowledge about a good amount of qualitative skills. The GMAT Quant topic in the problem-solving part requires calculative mathematical problems that should be solved with proper mathematical knowledge.

Solution and Explanation:

Approach Solution 1:

It is asked What is the current price of each towel? If the current price of each towel were to be increased by $1, 10 fewer of the towels could be bought for $120, excluding sales tax.

Evaluating further -

The first step is to establish some variables.
Q is the number of towels sold.
P is the cost per sold towel.
The next step is to create some equations.
We are aware that given the present cost:
PQ = 120
It is given that if the current price of each towel were to be increased by $1, 10 fewer of the towels could be bought for $120

This means
(P + 1)(Q – 10) = 120
The second equation should only be expressed in terms of P because we need to know the value of P. The PQ = 120 equation can be changed to achieve this. Consequently, we can state:
Q = 120/P
The equation (P + 1)(Q - 10) = 120 can now be solved by substituting 120/P for Q. There are now:

\((P + 1)(\frac{120}{P} – 10) = 120\)

Substituting values, we get:

\(120 – 10P + \frac{120}{P} – 10 = 120\)

\(–10P + \frac{120}{P} – 10 = 0\)

The denominators can be removed from the equation by multiplying the entire thing by P. This results in:

\(–10P^2 + 120 – 10P = 0\)

\(10P^2 + 10P – 120 = 0\)

\(P^2 + P – 12 = 0\)

(P + 4)(P – 3) = 0
P = -4 or P = 3
Since P can’t be negative, P = 3.

The answer is 3

Correct Answer: C

Approach Solution 2:

There is another approach to answering this question: It is asked What is the current price of each towel? If the current price of each towel were to be increased by $1, 10 fewer of the towels could be bought for $120, excluding sales tax.

Let Us assume the original cost of towels = x
This means

\(\frac{120}{x}-\frac{120}{[x+1]}= 10\)

\(120 = 10[x^2+x]\)

\([x^2+x-12]=0\)

[x + 4 ] [x - 3 ]
x = -4, 3
Since x can’t be negative, x = 3.

The answer is 3

Correct Answer: C

Approach Solution 3:

⇒  Let number of towels bought for $120 be n.

⇒  So price of single towel =$n120​

⇒  Now price of 1 towel increases by $1

⇒  So, new price of single towel =$n120​+1

⇒  Number of towel that could be bought at this price = n−10

⇒  So, new price of single towel = (n−10)120​

So, by equating both new price of single towel,

⇒  n120​+1=(n−10)120​

⇒  n(120+n)​=(n−10)120​

⇒  n2−10n−1200=0

⇒  (n−40)(n+30)=0

⇒  n=40 or n=−30

⇒  Number of towels is 40.

⇒ Current price per towel = 40120​=$3 

Correct Answer: C

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