Question 1201606
.
using 2 tractors a farmer can dig a farm in 20 days. He uses the 2 tractors 
for the first 8 days and added 6 more tractors to complete the work.
How long will it take to complete the work?
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                    Let' solve it MENTALLY.



<pre>
Two tractors complete the job in 20 days.

Hence, two tractors make  {{{1/20}}}  of the job per day.


Working first 8 day, two tractors made  {{{8/20}}}  of the job.

Hence,  1 - {{{8/20}}} = {{{(20-8)/20}}} = {{{12/20}}}  of the job remained.



    6 more added tractors make total 2+6 = 8 tractors, 
    which is 4 times as many as 2 tractors.

    Hence, 8 tractors will do  {{{4/20}}}  of the job per day.


It means that 8 tractors need  {{{((12/20))/((4/20))}}} = {{{12/4}}} = 3 days to complete the job.


<U>ANSWER</U>.  It will take 3 days to complete the job.
</pre>

Solved.