If Rohan bought 20 books at the rate of Rs. 120 each, 30 books at the rate of Rs. 150 each, and 15 books at the rate of Rs. 100 each, then find the average cost price per book.

1. A

   Rs. 133.79

2. B

   Rs. 134.45

3. C

   Rs. 178.61

4. D

   Rs. 129.23

Appeared in: UP CHO - 10 September 2021

Explanation

• The question requires calculating a weighted average, not a simple average, because the books were bought in different quantities at different prices.
• First, calculate the total cost for all books: (20 × 120) + (30 × 150) + (15 × 100) = 2400 + 4500 + 1500 = Rs. 8400.
• Next, calculate the total number of books purchased: 20 + 30 + 15 = 65 books.
• Finally, divide the total cost by the total number of books to find the average cost per book: Rs. 8400 / 65 = Rs. 129.23.

Why Other Options Were Wrong

• Option A: This value is incorrect and likely results from a calculation error during multiplication or addition of the total costs.
• Option B: This is an incorrect value that would be obtained through a miscalculation, possibly by dividing the correct total cost by an incorrect number of books.
• Option C: This value is significantly higher than the correct average and represents a major calculation error.

Related Visual

Clinical Relevance

• Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Calculation of weighted average cost as background academic context rather than a clinical decision trigger.
• While not a clinical question, this problem tests basic mathematical aptitude, a crucial skill for nurses.
• Nurses regularly use similar calculations for tasks such as determining correct drug dosages, calculating IV drip rates, and monitoring fluid intake and output.
• What if? - If Rohan had bought the 30 books at Rs. 120 instead of Rs. 150, the total cost would decrease significantly. The new total cost would be (20×120) + (30×120) + (15×100) = 2400 + 3600 + 1500 = Rs. 7500. The new average would be 7500 / 65 = Rs. 115.38.

How to Approach the Question

• First, identify that the question asks for an average cost where items are bought in different quantities at different prices. This indicates a weighted average is needed.
• Calculate the total cost for each group by multiplying the number of books by its corresponding price.
• Sum the costs of all groups to get the grand total cost.
• Sum the number of books in all groups to get the total quantity.
• Divide the grand total cost by the total quantity of books to find the average cost per book.
• Match your calculated average with the given options to find the correct answer.

Concept Tested & Keywords

• Concept Tested: Calculation of weighted average cost.
• Stem keywords: average cost price, books, rate
• Lead-in keywords: find

Question ID

QGaror75xhqhx6OzqdlJ8t

Copy ID