<PRE><B>Question 149079</B>
A plumber can install a dishwasher in 50 minutes. If the plumber brings his apprentice, the job takes 40 minutes. How long would it take the apprentice working alone.
:
Let a = time required if the apprentice works alone
:
Let the completed job = 1; 
:
{{{40/50}}} + {{{40/a}}} = 1
Multiply equation by 50a to get rid of the denominators, results:
40a + 50(40) = 50a(1)
:
40a + 2000 = 50a
:
2000 = 50a - 40a
:
2000 = 10a
a = {{{2000/10}}}
a = 200 min working alone
:
:
Check solution:
40/50 + 40/200 = 
4/5 + 1/5 = 1</PRE>