document.write( "Question 991887: A lorry tank was 3 / 5 full of petrol, 21 litres was then added and it is now 5 / 6 full. how many litres of petrol can the tank hold? \n" ); document.write( "
Algebra.Com's Answer #802092 by CubeyThePenguin(3113)\"\" \"About 
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x = number of gallons the tank can hold when full\r
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\n" ); document.write( "\n" ); document.write( "3x/5 + 21 = 5x/6\r
\n" ); document.write( "\n" ); document.write( "18x/30 + 21 = 25x/30\r
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\n" ); document.write( "\n" ); document.write( "-7x/30 = -21\r
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\n" ); document.write( "\n" ); document.write( "7x/30 = 21\r
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\n" ); document.write( "\n" ); document.write( "7x = 21*30\r
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\n" ); document.write( "\n" ); document.write( "x = 3 * 30 = 90
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