Question 1173832
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The other tutor showed a typical algebraic solution, using the fraction of the job that each worker completes in a day.<br>
Here is a quick informal solution, if formal algebra is not required.<br>
Doug can do the job alone in 3 days, so when he and his son complete the job together in 2 days, Doug does 2/3 of the job.
That means his son does 1/3 of the job in those 2 days.
And that means his son would take 2*3=6 days to do the job alone.<br>