document.write( "Question 1185956: Three brothers shared a box of biscuits.
\n" ); document.write( "Roy ate \"2%2F3\" of the box of biscuits and 1/3 of a biscuit.
\n" ); document.write( "Sam ate \"2%2F3\" of the remaining biscuits and 1/3 of a biscuit.
\n" ); document.write( "Tom ate \"2%2F3\" of the rest of the biscuits and 1/3 of a biscuit.
\n" ); document.write( "There were no biscuits left after this. How many biscuits did Roy a eat?
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Algebra.Com's Answer #816830 by greenestamps(13200)\"\" \"About 
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\n" ); document.write( "When each brother eats 2/3 of the biscuits, 1/3 of them are left. So when each brother eats some of the biscuits, the number of biscuits remaining gets multiplied by 1/3 and the reduced by 1/3. So

\n" ); document.write( "original number of biscuits: \"x\"

\n" ); document.write( "number after Roy eats his: \"%281%2F3%29x-1%2F3\"

\n" ); document.write( "number after Sam eats his: \"%281%2F3%29%28%281%2F3%29x-1%2F3%29-1%2F3\"

\n" ); document.write( "number after Tom eats his: \"%281%2F3%29%28%281%2F3%29%28%281%2F3%29x-1%2F3%29-1%2F3%29-1%2F3\"

\n" ); document.write( "The number of biscuits left at the end is 0, so

\n" ); document.write( "\"%281%2F3%29%28%281%2F3%29%28%281%2F3%29x-1%2F3%29-1%2F3%29-1%2F3=0\"

\n" ); document.write( "That equation is actually not too hard to solve, although it is easy to get lost along the way....

\n" ); document.write( "This kind of problem is quite often easier to work backwards, especially if there are a large number of steps. (Imagine what the final equation above would look like if there had been five (or more) brothers.)

\n" ); document.write( "At each step working the problem from beginning to end, the number of biscuits remaining is multiplied by 1/3 and then 1/3 is subtracted. Working that backwards, each step consists of adding 1/3 to the number remaining (the opposite of subtracting 1/3) and multiplying that by 3 (the opposite of dividing by 3).

\n" ); document.write( "Working the problem backwards is then simple:

\n" ); document.write( "biscuits remaining at the end: 0
\n" ); document.write( "biscuits remaining before Tom eats his: 3(0+1/3) = 3(1/3) = 1
\n" ); document.write( "biscuits remaining before Sam eats his: 3(1+1/3) = 3(4/3) = 4
\n" ); document.write( "biscuits remaining before Roy eats his: 3(4+1/3) = 3(13/3) = 13

\n" ); document.write( "There were 13 biscuits originally; Roy ate 9.

\n" ); document.write( "ANSWER: Roy ate 9 biscuits
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