<PRE><B>Question 1150748</B>
&lt;br&gt;
Tutor @ikleyn has shown the typical algebraic solution method for this kind of problem.&lt;br&gt;
Here are two alternative methods....&lt;br&gt;
(1) logical reasoning and some simple arithmetic....&lt;br&gt;
The worker who takes 8 hours to do the job alone takes twice as long as each of the others.  That means he works half as fast.&lt;br&gt;
So the three of them working together is like 2.5 workers working at the rate that it takes one of them to do the job alone.&lt;br&gt;
So the time it takes 2.5 workers to do the job at that rate is 4/2.5 = 8/5 hours.&lt;br&gt;
(2) using the least common multiple of the given times for the three workers....&lt;br&gt;
The numbers of hours for the three workers each to do the job alone are 8, 4, and 4.  The LCM of those numbers is 8.&lt;br&gt;
Consider what the three workers could do in 8 hours:&lt;br&gt;
The first worker could do the job once.
The second worker could do the job 8/4 = 2 times.
The third worker could do the job 8/4 = 2 times.&lt;br&gt;
So the three of them together in 8 hours could do the job 1+2+2=5 times.&lt;br&gt;
So the three of them can do the one job in 8/5 hours.&lt;br&gt;

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