text: A takes 3 hour more than B to walk 30 km. But if A doubles his pace, he is ahead of B by 3 /2 hours. Find their speed of walking
  
  Given:
  Distance = 30 km
  
  Let speed of A be = x km/h & speed of B be = y km/h
  
  Time taken by A to cover 30 km = 30/x
  [Time = Distance/Speed]
  
  Time taken by B to cover 30 km = 30/y
  
  30/x = 30/y + 3
  30/x – 30/y = 3———–(i)
  
  When A doubles his speed, then the time taken by A = 30/2x
  
  30/y = 30/2x + 3/2
  30/y – 30/2x = 3/2
  30/y – 15/x = 3/2————–(ii)
  
  Let us assume that 1/x = p & 1/y = q
  
  So equation (i) and equation (ii) becomes
  30p – 30q = 3——–(iii)
  30q – 15p = 3/2——–(iv)
  
  On adding equation (ii) and (iv) we get,
  
  30p – 30q = 3
  + (-15p) + 30q = 3/2
  _________________
  15p = 9/2
  p = 9/(2×15)
  p = 3/10
  
  Substituting the value of p = 3/10 in equation(iii) we get
  30p – 30q = 3
  30(3/10) – 30q = 3
  9 – 30q = 3
  -30q = -6
  q = 1/5
  
  Now we know that , 1/y = q
  1/y = 1/5
  y = 5km/h
  
  &, 1/x = p
  1/x = 3/10
  x = 10/3 km/h
  
  Hence
  A = 10/3 km/h
  B = 5 km/h
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