GMATT73 wrote:

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?

(1) 8 days

(2) 5 days

(3) 3 days

(4) 7 days

(5) 6 days

How long will it take for A alone to complete the job?

(1) 8 days

(2) 6 days

(3) 10 days

(4) 20 days

(5) 5 days

Q.1: Using the productivity to solve:

Let x,y,z be the work A,B and C can do in one day.

We have:

x+y=1/6

y+z=1/10

x+z=1/7.5

---> 2(x+y+z)= 1/6+1/10+1/7.5= 24/60=2/5 ---> x+y+z=1/5 -----> if they work together, they'll finish the work in 5 days

Q.2 (x+y)+(x+z)-(y+z)= 2x= 1/6+1/7.5 -1/10= 12/60=1/5---> x=1/10

----> A alone can finish the work in 10 days.