# Question #a4a8f

Oct 26, 2016

$4 \text{ hours " 16 2/3 " minutes}$

#### Explanation:

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 $\frac{1}{7}$ will be done.

Printer 2: whole job done in $11$ hours. In 1 hour $\frac{1}{11}$ will be done.

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

$\frac{1}{7} + \frac{1}{11} = \frac{11 + 7}{77}$

=$\frac{18}{77}$ of the full job $\left(\frac{77}{77}\right)$

the whole job will take $\frac{77}{77} \div \frac{18}{77}$

$\frac{77}{77} \times \frac{77}{18} = \frac{77}{18}$

=$4 \frac{5}{18}$ hours;

= $4 \text{ hours " 16 2/3" minutes}$