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Before the 62nd day, the original 10 workers had lost fived days to outages, meaning they had completed (61 – 5)) = 56 days of work. This means that half the work was completed in 56 days (112 days/2).
Once the 4 new workers joined, the speed of the work increased by 40% = 1.4 times. Now, the time required to complete remaining task worth 56 days = 56/1.4 = 40 days.
They therefore they needed 56 days for the first half of the task + 5 days of power outage + 40 days required to complete the second half of the task = 101 days. Since it actually took 102 days, they must have lost one additional day to power outage.
The correct choice is B.