Question 175570
Rey can do a story in 3 hours while Joe can do it in 5 hours.In how many hours can the two boys do the work , if they worked together? 
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Let t = time required if they work together
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Let the completed job = 1 (1 story)
:
{{{t/3}}} + {{{t/5}}} = 1
:
Multiply equation by a multiple of the two denominators, 15 will do this:
15*{{{t/3}}} + 15*{{{t/5}}} = 15(1)
5t + 3t = 15
:
8t = 15
t = {{{15/8}}}
t = 1.875 hrs or 1 hr 52.5 minutes
:
:
Check solution, replace t with 1.875 in original equation:
{{{1.875/3}}} + {{{1.875/5}}} = 1
.625 + .375 = 1.00