Question

If a and b together can complete a work in 18 days, a and c together in 12 days, and b and c together in 9 days, then b alone can do the work in:

Answer 1

1/a+1/b=1/18 first equation
1/a+1/c=1/12 second equation
1/b+1/c=1/9 third equation
in 1 and 3 equation keep 1/b in lhs and send the remaining to the
now add the equations
you will get 1/18-1/b+1/9-1/b=1/12
simplify it and you will get the answer as 12.5 days
hope so it's correct