A man completes 7/8 of a job in 21 days. How many more days will it take him to finish the job if quantum of work is further increased by 50% ?
- (a) 24
- (b) 21
- (c) 18
- (d) 15 ✓ UPSC's answer
Why the answer is (d)
• The man completes 7/8 of a job in 21 days, so his rate of work is (7/8) ÷ 21 = 1/24 of the job per day.
• The quantum of work is increased by 50%, making the total work 1.5 times the original, but he has already completed 7/8 of the original job.
• The remaining work to be done is 1.5 - 7/8 = 12/8 - 7/8 = 5/8 of the original job.
• At his rate of 1/24 of the job per day, the time required to complete 5/8 of the job is (5/8) ÷ (1/24) = (5/8) × 24 = 15 days.
• Therefore, it will take him 15 more days to finish the job, so the answer is option (d).
Why the other options are wrong
- (a) 24
- This option incorrectly calculates the remaining work or applies the wrong rate, resulting in an inflated number of days.
- (b) 21
- This option appears to assume he continues at the same pace for the same duration as the first 7/8, ignoring that the remaining work after the 50% increase is only 5/8 of the original job.
- (c) 18
- This option miscalculates the remaining work after the 50% increase, likely treating it as 3/4 instead of 5/8 of the original job.
Asked in the CSAT Paper II of the UPSC Civil Services Preliminary Examination 2021, held on 10 October 2021. Question and answer key: Union Public Service Commission. Explanation: UPSC Answer Check.