A ,B and C can do a work in 12, 15 and 20 days respectively. They started working together but after 4 days A left. In how many days will B and C complete the work.
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Answer: 6 days
Step-by-step explanation:
Lets assume total work to be done as 1.
Amt of work A can finish in a day = 1/12
Amt of work B can finish in a day = 1/15
Amt of work C can finish in a day = 1/20
Lets consider x as number of days taken to complete the work
A worked only for 4 days.
Hence, 4*(1/12)+x*(1/15+1/20) = 1
=> 1/3+x*(1/15+1/20) = 1
=> x*(1/15+1/20) = 1-1/3
=> x*(1/15+1/20) = 2/3
=> x*(4/60+3/60) = 2/3
=> x*7/60 = 2/3
=> x = (2/3)*(60/7)
=> x = 2*20/7
=> x = 40/7
=> x ≈ 6
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