The price of raw materials has gone up by 15%, labour cost has also increased GMAT Problem Solving

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Question: The price of raw materials has gone up by 15%, labour cost has also increased from 25% of the cost of raw material to 30% of the cost of raw material. By how much percentage should there be a reduction in the usage of raw materials so as to keep the cost same?

  1. 30%
  2. 24%
  3. 28%
  4. 25%
  5. 17%

“The price of raw materials has gone up by 15%” - this is a topic of the GMAT Quantitative reasoning section of GMAT. This question has been taken from the book "GMAT Official Guide Quantitative Review". To solve GMAT Problem Solving questions a student must have knowledge about a good number of qualitative skills. The GMAT Quant section consists of 31 questions in total. The GMAT quant topics in the problem-solving part require calculative mathematical problems that should be solved with proper mathematical knowledge.

Solution and Explanation:

Approach Solution 1:

Considering the given situation in the case of the price of raw materials increasing by 15%, and labour cost increasing from 25% to 30%, the initial approach can be used-
The initial price of raw materials = 100
The new price of raw materials = 115
Initial labour cost = 125
New labour cost = 130
Accordingly, the percentage at the rate of which it can be seen that reduction in the usage of raw materials so as to keep the cost same
For me, this meant that
115* 130 * x( % decrease) = 125 * 100
So just calculated the individual percentage decrease and added it
((130- 125) / 125) * 100 = 5/125 * 100 = 4
((115- 100) / 115) * 100 = 13
Total % = 17
Hence, 17% is the correct answer for option E

Correct Answer: E

Approach Solution 2:

Based on the given condition in the above question,
Let the initial cost of raw materials be 100. So, the initial labour cost was 25 and the net cost was 125
Now,
15% rise in raw materials cost and labour cost has gone up to 30% from 25 %
Raw material cost = 115 And
Labour cost = (115 × 30%) = 34.5
Accordingly. New net cost,
= 115 + 34.5 = 149.5
Difference of labour cost = 149.5 - 125 = 24.5
% reduction = 24.5×100149.5
= 17%
Hence there should be a 17% reduction in the usage of raw materials ensuring that the cost remains the same

Correct Answer: E

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