Question

It takes 12 men 5 days to complete a job.

(a) Work out how many days it would take 3 men to complete the same job.

I know that the answer is 20 but I need an explanation​

Answer 1

12 men, 5 days.
If you divide the amount of laborers by 4, you must multiply the time it takes by 4. Thus 12/4=3 men and 5*4= 20 days.