Question 768464
Kayla's copy store recived an order for 5,616 copies. The store has 3 printers. If Kayla only uses one printer at a time, 

the first printer would complete the job in 15 hours and 36 minutes, 
<pre>
That's 15·60 + 36 = 900 + 36 = 936 minutes

So the first printer's rate is 5616 copies per 936 minutes or {{{5616copies/(936minutes)}}} = 6{{{copies/minute}}}
</pre>
the second in 7 hours and 12 minutes, 
<pre>
That's 7·60 + 12 = 420 + 12 = 432 minutes

So the second printer's rate is 5616 copies per 432 minutes or {{{5616copies/(432minutes)}}} = 13{{{copies/minute}}}
</pre>
and the third in 11 hours and 42 minutes. 
<pre>
That's 11·60 + 42 = 660 + 42 = 702 minutes

So the third printer's rate is 5616 copies per 702 minutes or {{{5616copies/(702minutes)}}} = 8{{{copies/minute}}}
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How long would it take to process if all three printers were used at the same time?
<pre>
The combined rate of all three printers is 6+13+8 or 27 copies per minute.

27 copies is to 1 minute as 5616 copies is to x minutes:

{{{17/1}}}{{{""=""}}}{{{5616/x}}}

17x = 5616
  x = {{{5616/27}}} = 208 minutes = {{{208/60}}}hours = {{{3*28/60}}}hours = 3 hours 28 minutes.

Edwin</pre>