Bunuel wrote:
A started a work and left after working for 2 days. Then B did the remaining work in 9 days. Had A left the work after working for 3 days, B would have finished the remaining work in 6 days. In how many days can each of them working alone, finish the whole work?
A. A = 5 days and B = 15 days
B. A = 7 days and B = 21 days
C. A = 8 days and B = 18 days
D. A = 4 days and B = 12 days
E. A = 15 days and B = 15 days
Let the Rate of A = RA & the Rate of B = RB
2RA + 9RB = 1..............1
3RA + 6RB = 1..............2
equation 1 & 2
2RA + 9RB = 3RA + 6RB.............RA = 3RB
From 3 in 1
6RB + 9RB = 1.........15RB =1...........RB = 1/15..........Time taken by B alone = 15 days
RA= 3 * 1/15 = 1/5..........Time taken by A alone = 5 days
Answer: A
P.S.: Many ways to solve 2 equation with 2 unknowns. I chose to find relationship between RA & RB less time for me than solving 2 equations simultaneously.
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74% (02:10) correct 
Wish you all success
