In how many days B can finish the work alone? If
Answer: (3) 90 days
A can do in one day three times the work done by B in one day.
Then, A = 3 B
They together finish 2/5 of the work in 9 days.
Therefore, they together complete the work = 9 x 5/2
= 45/2 days
Then, 3/B + 1/B = 2/45
(3 + 1)/B = 2/45
4/B = 2/45
B = 4 x 45/2
B = 90 days
Then, the number of days by which B can do the work alone is 90 days.
Hence, the answer is (3) 90 days.