Answer:
20 hours
Step-by-step explanation:
Since 4 men as half as many as 8 men, it will take double the amount of time to perform the same amount of work. Therefore, it would take 20 hours to build the wall.
8 men takes 10hrs
1 man will take 8×10=80hrs
4 men will take lesser time than 1 person doing the same work alone hence time taken by them is 80/4=20hrs
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