Working Independently

[Abdulla]

Working independently, Susan can perform a task in 6 hours and Tom can perform it in 7 hours. If Susan and Tom work together at the task for 3 hours, at which point Susan leaves, how many hours will it take tom to complete the task alone?

(A) 1/14
(B) 2/5
(C) 1/2
(D) 29/42
(E) 1

OA is C

[earth@work]

Susan: 1 hour....... 1/6th work
Tom: 1 hour...........1/7th work
(tom+susan): 1 hour.........13/14th work
(tom+susan): 3 hour.........(13/14)*3 th work = 13/14
work left=1-13/14=1/14
Tom will take: (1/14)*7=1/2hour
answer C

[4meonly]

(tom+susan): 1 hour.........13/14th work
(tom+susan): 3 hour.........(13/14)*3 th work = 13/14

Small corrections:
(tom+susan): 1 hour.........13/42th work
(tom+susan): 3 hour.........(13/42)*3 th work = 13/14

[logitech]

3/6 + (3+x)/7 = 1

X=1/2

[mrsmarthi]

3/6 + (3+x)/7 = 1

X=1/2

Wow....that's an excellent short cut. So far I was trying to solve these type of problems in the routine elaborate way.

Kudos to you.

With the type of answers that you provide, Can't believe that you are targeting for 680. :roll:

Cheers.

[4meonly]

3/6 + (3+x)/7 = 1
X=1/2

SUPER!!!

logitech, please DO NOT schedule your GMAT till May!!!! We need you))))

[vivek.kapoor83]

Working independently, Susan can perform a task in 6 hours and Tom can perform it in 7 hours. If Susan and Tom work together at the task for 3 hours, at which point Susan leaves, how many hours will it take tom to complete the task alone?

(A) 1/14
(B) 2/5
(C) 1/2
(D) 29/42
(E) 1

OA is C

Suppose there is 42 unit of work. In 1 hr Susan do = 7 units, in 1 hr TOm do = 6 units.
together = 13 unit in 1 hr
and in 3hr = 39 units.
now, 3 units of work is left and he do 6 units in 1hr
therefore in 30mins he ll do = 3 units
Hence C.

[logitech]

3/6 + (3+x)/7 = 1
X=1/2

SUPER!!!

logitech, please DO NOT schedule your GMAT till May!!!! We need you))))

I will be around