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NCERT Class 12 · Ch 3 Exercise 3.2 · Q20

NCERT Class 12 Maths · Chapter 3 Matrices · Exercise 3.2 Question 20

A bookshop has 10 dozen chemistry, 8 dozen physics and 10 dozen economics books, sold at ₹80,₹60,₹40 each. Find total receipts using matrix multiplication.

💡 Concept Hints

  1. Check the matrix orders and the meaning of the requested operation before calculating.
  2. Keep row and column indices in order. Compare corresponding entries only after the matrix expressions have compatible dimensions.

✅ Step-by-Step Solution

Final Answer: ₹20160.
  1. Convert dozens to books: quantities are 120,96,120.
  2. For Total receipts, the inner dimensions agree: 3. Its order is 1×1. Use cᵢⱼ=Σₖaᵢₖbₖⱼ.
  3. Row 1: \(c_{11}=(120)(80) + (96)(60) + (120)(40)=20160\).
  4. Total receipts = \(\left[\begin{matrix}20160\end{matrix}\right]\).
  5. The 1×1 product is ₹20160.

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