Question
The cost of 9 biscuits and 12 namkeens together is Rs. 690, whereas cost of 6 biscuits and 15 namkeens together is Rs. 810. Find the cost of 3 namkeens.
Solution
Let the cost of a biscuit and a namkeen be Rs. 'a' and Rs. 'b', respectively.
So, 9a + 12b = 690 ------- (I)
And, 6a + 15b = 810 ------- (II)
On solving 2 * equation I - 3 * equation II,
We get, 2 x (9a + 12b) - 3 x (6a + 15b) = 2 x 690 - 3 x 810
Or, 18a + 24b - 18a - 45b = 1,380 - 2,430
Or, -21b = -1,050
Or, 'b' = 50
Therefore, required cost = 3 x 50 = Rs. 150
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