A fraction becomes 4 when 1 is added to both the numerator

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A fraction becomes 4 when 1 is added to both the numerator and denominator, it becomes 7 When 1 is subtract from both the numerator and denominator. The numerator of the given fractions is ?

1. 2
2. 3
3. 7
4. 15

Correct Option: D

Let the required fraction be p/q.
Then, (p +1) / (q +1) = 4
⇒ p - 4q= 3 ....(i)

And, (p - 1) / (q -1) = 7
⇒ p - 7q = -6 ....(ii)

Solving these equation we get p = 15, q=3