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Answer 1 · 2016-10-26T07:08:49

$4 " hours " 16 2/3 " minutes"$

If the printers are both working, the job will be done quicker.

Let's consider how much of the job each printer can do in $1$ hour.

Printer 1: whole job done in $7$ hours. In 1 hour $1/7$ will be done.

Printer 2: whole job done in $11$ hours. In 1 hour $1/11$ will be done.

If the printers are working together, then in one hour they will finish:
$1/7 +1/11$ of the total job.

$1/7 +1/11 = (11+7)/77$

= $18/77$ of the full job $(77/77)$

the whole job will take $77/77 div 18/77$

$77/77 xx 77/18 = 77/18$

= $4 5/18$ hours;

= $4 " hours " 16 2/3" minutes"$