Question : The present ages of A and B are in the ratio 3 : 4. Twelve years ago, their ages were in the ratio 2 : 3. The sum of the present ages of A and B (in years) is:
Option 1: 72
Option 2: 60
Option 3: 84
Option 4: 48
Correct Answer: 84
 
  Solution :
 
 Let the present ages A and B be 3$x$ and 4$x$
 
  Present  age of ratio = 3 : 4
  
  Before 12 years the ratio of ages A and B =  2 : 3
  
  According to the question,
  
  ⇒ $\frac{(3x - 12)}{4x - 12)}$ =  $\frac{2}{3}$
  
  ⇒ $3(3x − 12) = 2(4x − 12)$
  
  ⇒ $9x − 36 = 8x − 24$
  
  ⇒ $x − 36 = −24$
  
  ⇒  $x$ = 12
  
  A's present age = 3$x$ = 3 × 12 = 36 years
  
  B's present age = 4$x$ = 4 × 12 = 48 years
  
  So, the sum of the present ages of A and B = 36 + 48 = 84 years
  
  Hence, the correct answer is 84.
 
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