Four pens and five erasers cost Rs. 128. Five pens and four erasers cost Rs. 124. Find the cost of each pen (in Rs.).
Explanation:
Let the costs of each pen and each eraser be Rs. p and Rs. e respectively
∴ 4p + 5e = 128 …(1)
∴ 5p + 4e = 124 …(2)
Adding (1) and (2),
⇒ 9 × (p + e) = 252
⇒ p + e = 28 …(3)
Subtracting (1) from (2),
⇒ p - e = - 4 …(4)
Adding (3) and (4),
⇒ 2p = 24
⇒ p = 12.
Hence, option (b).
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