Question 716622
kris can do a piece of work in 6 hours 
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So Kris's work rate is 1 job per 6 hours or {{{1_job/(6_hr)}}} = {{{1/6}}}{{{job/hr}}}
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matt can complete the same piece of work in 4 hours
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So Matt's work rate is 1 job per 4 hours or {{{1_job/(4_hr)}}} = {{{1/4}}}{{{job/hr}}}
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how long will it take them to do a piece of work if they work togrther at the same rates?
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Let the answer be x hours.
So their combined work rate is 1 job per x hours or {{{1_job/(x_hr)}}} = {{{1/x}}}{{{job/hr}}}

The equation comes from:

            {{{(matrix(7,1,
"Kris's",work,rate,in,jobs,per,hour))}}}{{{""+""}}}{{{(matrix(7,1,
"Matt's",work,rate,in,jobs,per,hour))}}}{{{""=""}}}{{{(matrix(8,1,
"their",combined,work,rate,in,jobs,per,hour))}}}

                            {{{1/6}}}{{{""+""}}}{{{1/4}}}{{{""=""}}}{{{1/x}}}

Multiply through by LCD = 12x and get 2.4 hours or 2 hours and 24 minutes.


Edwin</pre>