Working together, A and B can do a job in 6 days. B and C can do the same job in 10 days, while C and A can do it in 7.5 days. How long will it take if all A, B and C work together to complete the job?
Answer: D
Given that A and B can complete the work in 6 days A + B will do 1/6 of the work in 1 day => A + B = 1/6 ---> (1)
B and C can do the same job in 10 days, B + C will do 1/10 of the work in 1 day => B + C = 1/10 ---> (2)
C and A will do the same job in 7.5 days i.e., 15/2 days C + A will do 2/15 of the work in 1 day => C+ A = 2/15 ---> (3)
Adding all the above three equation we get 2 ( A + B + C ) = 1/6 + 1/10 + 2 /15 = 5/30 + 3/ 30 + 4 / 30 = 12 / 30 => A + B + C = 6 / 30 = 1 / 5
In one day A, B and C can finish 1/5 of the work => working together they will finish the work in 5 days.