Join 60,000+ competitive exam aspirants
or with email
Your Cart
Subtotal₹0
Total₹0
Examoogle • User • info@examoogle.com • EE-2024-8821
Chapter 1 of 12 • Page 1 of 248🔒 Protected PDF • Watermarked
Join 60,000+ competitive exam aspirants
A and B can complete a job in 12 days and 18 days, respectively. If they work together for 6 days, how much of the job is left to be done?
91 of the job
71 of the job
21 of the job
61 of the job
61 of the job
Calculate LCM of (12, 18) = 36 units. A's efficiency = 3, B's efficiency = 2. Combined = 5. In 6 days, they finish 5 × 6 = 30 units. Left = 36 - 30 = 6 units. Fraction left = 6/36 = 1/6.
Time taken by A = 12 days, Time taken by B = 18 days, Duration worked together = 6 days.
Work=TotaltimeTimeworked
Calculate LCM of (12, 18) = 36 units. A's efficiency = 3, B's efficiency = 2. Combined = 5. In 6 days, they finish 5 × 6 = 30 units. Left = 36 - 30 = 6 units. Fraction left = 6/36 = 1/6.
Many students calculate the work done (30/36 = 5/6) and mark it as the answer, forgetting the question asks for the work 'left to be done'.
Calculate Total Work
Assuming total work is the Least Common Multiple (LCM) of 12 and 18, which is 36 units.
Total Work=36units
Determine Individual Efficiencies
Efficiency is Work/Time. A's efficiency = 36/12 = 3 units/day. B's efficiency = 36/18 = 2 units/day.
(A+B)eff=3+2=5units/day
Calculate Work Completed
In 6 days of working together, total work completed is 6 days multiplied by combined efficiency.
Workdone=5×6=30units
Calculate Remaining Work
Subtract the completed work from total units and find the fraction of the job left.
Workleft=3636−30=366=61
D is correct because 30 out of 36 units of work were completed, leaving 6 units, which is 1/6 of the total job.
This LCM efficiency technique is identical to calculating the combined pipe fill rate in Pipe and Cistern problems.