Answer:
135 days
Explanation:
Often, we measure work in man·days. This piece of work requires ...
(45 man)·(90 days) = 4050 man·days
When there are only 30 men, the number of days required can be found by dividing this work by the number of men:
4050 man·days/(30 man) = 135 days
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Another approach is to realize the time is inversely proportional to the number of men. If the number of men is 30/45 = 2/3 the original, then the time will be 3/2 the original, or ...
(3/2)·90 days = 135 days.