Question 120561
Jerry worked for one day on a project that he could have completed alone in nine days. Bill joined Jerry the next day, and they worked together for exactly three days to complete the project. How much of the job did Bill do in those three days? Express you answer as a common fraction.
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I would do it this way:
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Let the completed job = 1
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WE know Jerry's share = 4/9 (he worked 4 days)
Let Bills share = 3/x  (he worked 3 days)
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{{{4/9}}} + {{{3/x}}} = 1
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Multiply equation by 9x to get rid of the denominators
9x*{{{4/9}}} + 9x*{{{3/x}}} = 9x(1)
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Cancel out the denominators and we have:
4x + 9(3) = 9x
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27 = 9x - 4x
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27 = 5x
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x = 27/5
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x = 5.4 
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Bills fraction: {{{3/5.4}}} = {{{30/54}}} = {{{5/9}}} is Bill's share of the work
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We can check that
(4/9) + (5/9) = 1, the completed job