Question 978598
It takes 5 hours for Anthony to fix a drain pipe.
<pre>
So Anthony's drain pipe fixing rate is 1 drain pipe fixed per 5 hours =

{{{matrix(1,4,1, drain, pipe, fixed)/matrix(1,2,5,hr)}}}{{{""=""}}}{{{matrix(1,2,1/5,matrix(1,3, drain, pipe, fixed)/(hr)))}}} 
</pre>
How many hours will it take for the assistant to do the job alone?
<pre>
Let the answer be x hours.  Then the assistant's drain pipe fixing rate is
1 drain pipe fixed per x hours =

{{{matrix(1,4,1, drain, pipe, fixed)/matrix(1,2,x,hr)}}}{{{""=""}}}{{{matrix(1,2,1/x,matrix(1,3, drain, pipe, fixed)/(hr)))}}} 
</pre>
If his assistant helps him, it takes 3 hours.
<pre>
Then their combined drain pipe fixing rate is 1 drain pipe fixed per 3 hours =

{{{matrix(1,4,1, drain, pipe, fixed)/matrix(1,2,3,hr)}}}{{{""=""}}}{{{matrix(1,2,1/3,matrix(1,3, drain, pipe, fixed)/(hr)))}}} 
 
The equation comes from 

{{{(matrix(4,1,

"Anthony's",drain_pipe,fixing,rate))}}}{{{""+""}}}{{{(matrix(5,1,

his,"assistant's",drain_pipe,fixing,rate))}}}{{{""=""}}}{{{(matrix(5,1,

their,combined,drain_pipe,fixing,rate))}}}

       {{{1/5}}}{{{""+""}}}{{{1/x}}}{{{""=""}}}{{{1/3}}}

Multiply through by the LCD of 15x and solve for x.

Edwin</pre>