Question

A, B together do a job in 6 days, B, C together do the same job in 10 days, C, A together do
the same job in 7.5 days. If all three work together in how many days will they complete
the job?

Answer 1

Answer:

5 days

Step-by-step explanation:

A and B can do a job in 6 days. They complete 1/6th of the job in a day.  

i.e.

1 /A + 1 /B = 1 /6  ------- -- (1)

Similarly, B and C will complete 1 /10 th of the job in a day.  

i.e  

1 /B + 1 /C = 1 /10  ---------- (2)

And C and A will complete  1 /7.5  or  2 /15 th of the job in a day  

i.e  

1 /C + 1 /A = 2 /15  ------------ (3).

Adding (1), (2) and (3) we get:  

1/A+1/B+1/C= 1/5

i.e working together, A, B and C complete 1 /5 th of the job in a day.  

Therefore, they will complete the job in 5 days.

Answer 2

Answer:11.75days

Step-by-step explanation

A+B=6DAYS

B+C=10DAYS

C+A=7.5DAYS

2(A+B+C)=23.5DAYS

A+B+C=(23.5÷2)=11.75DAYS