Question #a4a8f

Question

1399 views around the world

You can reuse this answer
Creative Commons License

Answer 1 · 2016-10-26T07:08:49

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

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 $1$ $1$ hour.

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

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

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

$\frac{1}{7} + \frac{1}{11} = \frac{11 + 7}{77}$ $1/7 +1/11 = (11+7)/77$

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

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

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

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

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