Question
In a class, the ratio of number of boys to number of
girls is 15:11. If 3 boys joined the class and 1 girl left the class, then the ratio becomes 7:5. Find the actual number of girls in the class.Solution
Let initially the number of boys and girls be 15x and 11x, respectively.
(15x + 3) : (11x − 1) = 7 : 5
Or, 5(15x + 3) = 7(11x − 1)
Or, 75x + 15 = 77x − 7
Or, 2x = 22 ⇒ x = 11
Therefore, number of girls = 11 × 11 = 121
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