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David typically takes 3 hours less than Marilyn to build a shelf if each work alone. David and Marilyn worked together to build shelf for 1 hour, and then Marilyn finished the job without David after an additional 3 hours. How long would it have taken David to build the shelf alone ?

 Feb 1, 2020
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D time =  M time -3       rate =  1/(M-3)

 

 

(1/(m-3)  + 1/m)(1 hr)   + 1/m (3 hr)   = 1 shelf   Use quadratic formula to

Solve for m = 6      then  d = 3   hrs to build alone

 Feb 1, 2020

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