Final answer:
To find out how long it takes one man to complete the job, you multiply the time it takes 20 men by 20, resulting in 600 days.
Explanation:
To determine how long it will take one man to complete the job, you need to consider that 20 men can complete the job in 30 days. This means 1 man will take 20 times longer, so it will be 20 times 30 days. Therefore, it will take 1 man 600 days to complete the job alone.
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