document.write( "Question 477023: two candles of the same height are lit at the same time. each candle burns at a constant rate and the first candle takes 5 hours while the second candle takes 4 hours to burn completely. find the time, in hours, taken for the height of the first candle to be four time that of the second candle \n" ); document.write( "
Algebra.Com's Answer #327061 by josmiceli(19441)\"\" \"About 
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Let \"+h%5B0%5D+\" = the height that both candles start at
\n" ); document.write( "Let \"+h%5B1%5D+\" = the current height of the 1st candle
\n" ); document.write( "Let \"+h%5B2%5D+\" = the current height of the 2nd candle
\n" ); document.write( "Let \"+t+\" = the current time expired in hours
\n" ); document.write( "given:
\n" ); document.write( "\"+h%5B0%5D+%2F+5+\" = the rate of burning of the 1st candle
\n" ); document.write( "\"+h%5B0%5D+%2F+4+\" = the rate of burning of the 2nd candle
\n" ); document.write( "-------------
\n" ); document.write( "For the 1st candle:
\n" ); document.write( "(1) \"+h%5B1%5D+=+h%5B0%5D+-+%28+h%5B0%5D%2F5+%29%2At+\"
\n" ); document.write( "For the 2nd candle:
\n" ); document.write( "(2) \"+h%5B2%5D+=+h%5B0%5D+-+%28+h%5B0%5D%2F4+%29%2At+\"
\n" ); document.write( "--------------
\n" ); document.write( "given:
\n" ); document.write( "\"+h%5B1%5D+=+4h%5B2%5D+\"
\n" ); document.write( "(1) \"+4h%5B2%5D+=+h%5B0%5D%2A%281+-+t%2F5%29+\"
\n" ); document.write( "(1) \"+h%5B2%5D+=+%28+h%5B0%5D%2A%281+-+t%2F5%29%29%2F4+\"
\n" ); document.write( "and
\n" ); document.write( "(2) \"+h%5B2%5D+=+h%5B0%5D%2A%281+-+t%2F4%29+\"
\n" ); document.write( "------------------------
\n" ); document.write( "I can set the right sides equal to each other
\n" ); document.write( "\"+%28+h%5B0%5D%2A%281+-+t%2F5%29%29%2F4+=+h%5B0%5D%2A%281+-+t%2F4%29+\"
\n" ); document.write( "Divide both sides by \"+h%5B0%5D+\"
\n" ); document.write( "\"++%281+-+t%2F5%29%2F4+=+1+-+t%2F4+\"
\n" ); document.write( "Multiply both sides by \"4\"
\n" ); document.write( "\"+1+-+t%2F5+=+4+-+t+\"
\n" ); document.write( "Multiply both sides by \"5\"
\n" ); document.write( "\"+5+-+t+=+20+-+5t+\"
\n" ); document.write( "\"+4t+=+20+-+5+\"
\n" ); document.write( "\"+4t+=+15+\"
\n" ); document.write( "\"+t+=+3.75+\"
\n" ); document.write( "It will take 3 hrs and 45 min for the
\n" ); document.write( "1st candle to be 4 times as high as the 2nd candle
\n" ); document.write( "check answer:
\n" ); document.write( "Suppose the heights of both start at 1 m
\n" ); document.write( "For the 1st candle:
\n" ); document.write( "For the 1st candle:
\n" ); document.write( "(1) \"+h%5B1%5D+=+1+-+%28+1%2F5+%29%2A3.75+\"
\n" ); document.write( "(1) \"+h%5B1%5D+=+1+-+.2%2A3.75+\"
\n" ); document.write( "(1) \"+h%5B1%5D+=+1+-+.75+\"
\n" ); document.write( "(1) \"+h%5B1%5D+=+.25+\"
\n" ); document.write( "For the 2nd candle:
\n" ); document.write( "(2) \"+h%5B2%5D+=+1+-+%28+1%2F4+%29%2A3.75+\"
\n" ); document.write( "(2) \"+h%5B2%5D+=+1+-+.25%2A3.75+\"
\n" ); document.write( "(2) \"+h%5B2%5D+=+1+-+.9375+\"
\n" ); document.write( "(2) \"+h%5B2%5D+=+.0625+\"
\n" ); document.write( "and
\n" ); document.write( "\"+h%5B1%5D+%2F+h%5B2%5D+=+.25%2F.0625+\"
\n" ); document.write( "\"+h%5B1%5D+%2F+h%5B2%5D+=+4+\"
\n" ); document.write( "OK
\n" ); document.write( "
\n" );