Two friends have ages in ratio $5:7$. After $4$ years the ratio becomes $3:4$. Present age of younger is

Two friends have ages in ratio $5:7$. After $4$ years the ratio becomes $3:4$. Present age of younger is
  1. $20$
  2. $28$
  3. $15$
  4. $24$

Solution

Ages $5k, 7k$. $\dfrac{5k+4}{7k+4} = \dfrac{3}{4} \Rightarrow 4(5k+4) = 3(7k+4) \Rightarrow 20k+16 = 21k+12 \Rightarrow k = 4$. Younger $= 20$.

Asked in: MH-SSC-9

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