Join 60,000+ competitive exam aspirants
or with email
Your Cart
SubtotalтВ╣0
TotalтВ╣0
Examoogle тАв User тАв info@examoogle.com тАв EE-2024-8821
Chapter 1 of 12 тАв Page 1 of 248ЁЯФТ Protected PDF тАв Watermarked
Join 60,000+ competitive exam aspirants
A and B working alone can do a work in 40 days and 30 days, respectively. They started the work together, but B left after some time and A finished the remaining work in 5 days. How many days after starting did B leave the work?
12 days
14 days
15 days
16 days
15 days
Calculate LCM of 40 and 30 (120 units). Subtract A's work in the final 5 days (5├Ч3=15 units) from total, then divide the remainder (105 units) by the combined efficiency of A and B (3+4=7).
A alone takes 40 days, B alone takes 30 days to finish the work. B leaves after some time and A completes the remaining work in 5 days.
Work=Efficiency├ЧTime
Calculate LCM of 40 and 30 (120 units). Subtract A's work in the final 5 days (5├Ч3=15 units) from total, then divide the remainder (105 units) by the combined efficiency of A and B (3+4=7).
Students often calculate the total days worked by B instead of identifying the days they worked together by subtracting the A-only phase.
Calculate Total Work and Efficiencies
Assume total work is the LCM of 40 and 30, which is 120 units. A's daily efficiency is 120/40=3 units/day, and B's is 120/30=4 units/day.
W=120,EAтАЛ=3,EBтАЛ=4
Determine Work Done by A Alone
A finishes the remaining work alone in 5 days. Work done by A in 5 days is 5├Ч3=15 units.
WAтАЛ=5├Ч3=15
Calculate Time B Worked Together with A
Remaining work done together is 120тИТ15=105 units. Their combined efficiency is 3+4=7 units/day. The time they worked together is 105/7=15 days.
T=3+4120тИТ15тАЛ=15
C is correct because the calculation shows that B worked for 15 days before leaving the work.
This concept is identical to pipe and cistern problems where one pipe is closed after some time; treating 'negative' flow as work deduction follows the same logic.
Get instant step-by-step AI explanations, full shift Previous Year Papers (SSC GD, RRB, SSC JE), and regional rank analysis on the official Examoogle App.
Free Download тАв 100K+ Aspirants