Question 1152573
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There are of course many different ways to solve the problem.  The solution from the other tutor uses formal mathematics, which is fine.<br>
I prefer a less formal solution using common sense, like this:<br>
Half the house was built by 4 workers in 5 days.  So 20 man-days builds half of a house.<br>
The other half remains to be built; it will require another 20 man-days.<br>
They want to finish in 2 days; the number of workers required is 20/2 = 10.<br>
There are currently 4 workers; the number of additional workers required is 10-4=6.<br>