There are 2 Candle of same heights. Both are lit at the same time.
They burn completely within 4 hours and 3 hours respectively.Both candles burn at constant speed.After so long, the height of the 1st candle will be twice the height of the 2nd candle.

• If initial height of both candles is 1 unit, and
  the height of the 1st candle will be twice the height of the 2nd candle after x hrs, then
  (1-x/4)= 2*(1-x/3)= 2-2x/3
  1= 2x/3-x/4 = 5x/12
  x=12/5 hrs = 2 2/5 hrs = 2 hrs 24 mins
  
• 12 years agoHelpfull: Yes(3) No(0)
• let height of candles is L.C.M. (3,4)= 12 units
  height of the 1st candle will be twice of 2nd candle after t hrs
  ATQ, (12-4t) : (12-3t)=1:2
  => t = 12/5 hrs
  => t = 2 hrs 24 mins
• 12 years agoHelpfull: Yes(3) No(0)