A is $7$ years older than B. After $4$ years their ages will be in ratio $5:4$. Present age of B is

A is $7$ years older than B. After $4$ years their ages will be in ratio $5:4$. Present age of B is
  1. $24$
  2. $28$
  3. $20$
  4. $32$

Solution

$\dfrac{x+11}{x+4} = \dfrac{5}{4} \Rightarrow 4x + 44 = 5x + 20 \Rightarrow x = 24$.

Asked in: IMO

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