Well, this is how I would solve the problem:

Statement 1:

Sally takes 4k+7 hrs to complete the thing alone.

So time taken by Sally = 11, 15, 19, 23 or 27 hrs.

We know nothing about how fast George and Andy work!

Thus - NOT SUFFICIENT!

Statement 2:

George - 2k+1 hr

Time - 3, 5, 7, 9 or 11

Andy - 3+2k

Time - 5, 7, 9, 11 or 13

Assume the worst case scenario - Only George and Andy are working and they're both taking their own sweet time:

Therefore, time : 13x11/(13+11) = 13x11/24 = 143/24

Quick Math:

24x8 = 192

Thus, 143/24 is less than 8 :D

Which means:

George and Andy can finish the job before the 8hr deadline if they work together (irrespective of how fast or slow they work and independent of Sally's work rate!)

Ans: B

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From 650 to 710 to 750 - My Tryst With GMAT [Experience Thread]