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Example 6 Romila went to a stationery shop and purchased 2 pencils & 3 erasers for Rs 9. Her friend Sonali saw the new variety of pencils and erasers with Romila, and she also bought 4 pencils and 6 erasers of the same kind for Rs 18. Find the cost of each pencil and each eraser. Let the Cost of Pencil be Rs x & Let the Cost of Eraser be Rs y Given that Romila purchased 2 pencils & 3 erasers for Rs 9 2 × (Cost of pencil) + 3 × (Cost of eraser) = 9 2x + 3y = 9 Also, Her friend Sonali saw the new variety of pencils and erasers with Romila, and she also bought 4 pencils and 6 erasers of the same kind for Rs 18 Sonali purchased 4 pencils and 6 erasers for Rs 18 4 × (Cost of pencil) + 6 × (Cost of eraser) = 18 4x + 6y = 18 Thus, our equations are 2x + 3y = 9 ...(1) 4x + 6y = 18 …(2) From (1) 2x + 3y = 9 2x = 9 – 3y x = ((𝟗 − 𝟑𝒚)/𝟐) Putting value of x in (2) 4x + 6y = 18 4 ((9 − 3𝑦)/2)+6𝑦=18 2 (9 – 3y) + 6y = 18 18 – 6y + 6y = 18 18 = 18 It is true for all values of x & y. Since the given equations have infinitely many solutions, That is why we cannot obtain a unique solution Since the given equations have infinitely many solutions, That is why we cannot obtain a unique solution

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Davneet Singh

Davneet Singh has done his B.Tech from Indian Institute of Technology, Kanpur. He has been teaching from the past 14 years. He provides courses for Maths, Science and Computer Science at Teachoo