work

[bmwhype]

A completes the given task in 12 hours.
B completes the given task in 9 hours.
A does the work for 1/3 of the work working at a conistant rate. Then B joins him for the rest of the work. How many hours did it take A to complete the task?

[coyote]

For the first 1/3rd work A will take 4hours.
Then both A and B will complete (1/12) + (1/9) fraction of work in 1 hour.
Hence they will finish remaining 2/3rd work in (2/3) / (7/36) hours = 24/7 hours.

Total time = 7 hours 3/7 minutes.

What's the OA?

[wizind77]

A's rate = W/12 per hour
B's rate = W/9 per hour

time taken - A alone for W/3 = ( W/3 / W/12) = 4hrs
time taken - A+B for 2W/3 = ( 2W/3 / 7W/36 [ w/12+w/9]) = 24/7 hrs

total = 4 + 24/7 = 52/7 hrs

[agma]

So, we have total time, but we need to find How many hours did it take A to complete the task?

[wizind77]

So, we have total time, but we need to find How many hours did it take A to complete the task?

total = 52/7 or 7 3/7 hrs or 7hrs 3/7 *60 min.

[agma]

Thanks!

[agma]

1/9 + 1/12 = 1/x where x = combined time; x =36/7

4 + (2/3) * (36/7) = 4+24/7 = 52/7
thanks again

[bmwhype]

nice everyone got it correct. i made this Q up. my answer was approx 7 hours and 26 minutes

[narinder82]

Ans is 4 + 24/7 Hours