Answer : 1 50 days Explanation : Answer: A) 50 days Explanation: 50 men can build a tank in 40 days Assume 1 man does 1 unit of work in 1 dayThen the total work is 50×40 = 2000 units 50 men work in the first 10 days and completes 50×10 = 500 units of work45 men work in the next 10 days and completes 45×10 = 450 units of work40 men work in the next 10 days and completes 40×10 = 400 units of work35 men work in the next 10 days and completes 35×10 = 350 units of workSo far 500 450 400 350 = 1700 units of work is completed and Remaining work is 2000 - 1700 = 300 units 30 men work in the next 10 days. In each day, they does 30 units of work. Therefore, additional days required = 300/30 =10 Thus, total 10 10 10 10 10 = 50 days required.

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