A man can do a piece of work in 80 days. He started doing the work and on every successive day, he does twice the amount of work done on the previous day. If he goes on at the same rate, in how many days will he be able to complete the work?
Explanation:
Assuming he can do 1 unit of work every day.
∴ Total work done in 80 days = 80 × 1 = 80 units.
Now, when his efficiency doubles every day.
Work done till day 1 = 1 unit. Work done till day 2 = 1 + 2 = 3 units. Work done till day 3 = 3 + 4 = 7 units. Work done till day 4 = 7 + 8 = 15 units. Work done till day 5 = 15 + 16 = 31 units. Work done till day 6 = 31 + 32 = 63 units. Work done till day 7 = 63 + 64 = 127 units.
Since only 80 units of work is to be complete, it would get completed on 7th day.
Hence, 7.
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