There are 3 candles each burns for 60 mins and you have to calculate 90 mins by burning all the candles.

• light 1st candle from both ends it will burn in 30 min
  as 1st candle lasts,light 2nd candle from both ends & as 2nd lasts,light 3rd from both ends
  so,burning time for 3 candles= 30+30+30=90 min can be calculated.
  
• 10 years agoHelpfull: Yes(46) No(0)
• light the first candle ,it will take 60 min and then light up two candles at the both the ends it will take 30 min.So 60+30=90
• 10 years agoHelpfull: Yes(7) No(1)
• 1st candle-60minutes
  2nd candle-15mintues after 1st candle is ignited(Now total time taken to burn both candle is 75 minutes)
  3rd candle-15mintues after 2nd candle is ignited(now total time taken to burn 3 candles is 90 minutes)
• 10 years agoHelpfull: Yes(6) No(9)
• simple, light one candle it will brown out in 60min then burn another candle at both ends so that it will burn out in 30min.so total 60+30=90. or
  by burning all the candles one by one at both ends.
  
• 10 years agoHelpfull: Yes(5) No(6)
• burn the first two candles at a time as they take 60 min, burn 3rd candle when the previous candles are half burnt
• 10 years agoHelpfull: Yes(3) No(2)
• light each candle from both the sides.....implies it takes 30 min....so 30*3=90 min..:D
• 10 years agoHelpfull: Yes(2) No(0)
• bur 1st candle for 30mins aftr 30mins burn 1st candle along wit remaining 2
• 10 years agoHelpfull: Yes(1) No(3)
• he just divide all 3 candles into 2 parts
  
  now they have 6 candles each can burn for 30 mins
  
  burn two candles for first 30 mins
  
  then burn other 2 candles for next 30 mins
  
  and finally burn last 2 candles for last 30 mins
  
  and when that all candles are over exactly 90 mins are also over
• 10 years agoHelpfull: Yes(1) No(0)
• Light every candle from both sides.....considering it will take 30 mins to burn one candle....30*3=90.
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• light the first candle and watch it if it reaches its half light the 2nd one and watch it again if it reaches its half light the 3rd one and to its half
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• burn all d three at the same time from both the ends 30+30+30=90
• 10 years agoHelpfull: Yes(0) No(5)
• first burn one candle and when it reaches its half then burn the other two candles together
  
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• put all the candles in row and burn both ends of row
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• if the first candle start at the time of begining,after 15 min burn the 2nd candle and after 15 burn the 3rd candle then total time for burning the candles=90min
• 10 years agoHelpfull: Yes(0) No(1)
• light 2 candles simultaneously....when they are half that means 30 mins are over and then light 3rd candle and burn it fully....then remaining 60 mins are calculated....and in between these 60 mins of 3rd candle the first 2 candles are also burn out
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• first burn a candle(60 min) then burn the second one on both sides so it burns at a double rate (i.e. 30 min)so sum is 90 min
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• burn the 3 candles one by one and divide the total time by 2.
• 10 years agoHelpfull: Yes(0) No(0)
• 1st candle starts burning,then lit 2nd candle after 10 mins,then lit 3rd candle after 20 mins of first candle(20 mins after 2nd candle lit) then third candle takes 60 mins to burn from 30th minute to 90th minute
• 10 years agoHelpfull: Yes(0) No(1)
• burn 1st and scond candle together so it will take 60 minutes to burn.Just after 30 mins burn third candle.so frist 2 cburns completly in 60minutes while third is half burnt
  
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• light all the candles at a time. when they reach half of the height it is 90min
  
• 10 years agoHelpfull: Yes(0) No(0)
• each candle burns for 60 mins
  therefore burn each candle at both sides
  so 30+30+30=90 mins
• 10 years agoHelpfull: Yes(0) No(0)
• Burn the candel from both the ends.Hence one single candle will burn in 30 minutes.so three candels will burn in 90 minutes
• 10 years agoHelpfull: Yes(0) No(0)
• Burn first& second candle at same time so that it will take 60 mins after the 1st&2nd over burn the third candle at both sidee so that it will take it will take 30 mins .Then totally 90 minutes have calculated
• 10 years agoHelpfull: Yes(0) No(0)
• lit a candle after it remains a 1/4 part...lit another...as it compltes 1/4 part lit another one and let its half to be completed.
  or lit all the three candles bothsides one by one...
• 10 years agoHelpfull: Yes(0) No(0)
• first light 2 candles at a time untill they becime half by checking with the unlighted third candle,,whey they reach to the half of the length,,it means 30 minutes have gone,at that moment light the other candle ,after 30 minutes 1st and 2nd candles complte burniing,,and 3 rd candle remains to half of the length,,nd after 30 minutes the 3 rd candle will too burns comlpetly
• 9 years agoHelpfull: Yes(0) No(0)
• burn two candles as it is..burn the 3rd one from both the sides
  
• 9 years agoHelpfull: Yes(0) No(0)
• light up the candles from both ends that makes each candle burn up in 30 minutes
  so total time for 3 candles to burn is 90 minutes
• 8 years agoHelpfull: Yes(0) No(0)
• burn the first candle till it reaches 1/4 of its size then light the 2nd one and wait till it reaches 1/4 and light the 3rd candle.
• 8 years agoHelpfull: Yes(0) No(1)
• light 1st candle from both ends it will burn in 30 min
  as 1st candle lasts,light 2nd candle from both ends & as 2nd lasts,light 3rd from both ends
  so,burning time for 3 candles= 30+30+30=90 min can be calculated.
• 1 year agoHelpfull: Yes(0) No(0)