A can complete a certain job in 12 days. B is 60% more efficient than A. In how many days can B complete the same job?

B is 60% more efficient than A, which means that the rate of B is 1.6 times as greater as that of A.
So, if A can complete the job in 12 days,
then B completes the same job in 12/1.6 = 12/(8/5)
= 15/2
= 7.5 days.

Alternative method:
Ratio of times taken by
A and B = 160 : 100 = 8 : 5
Suppose B alone takes x days to do the job.
Then, 8 : 5 :: 12 : x
or, 8x = 5 × 12
or, x = 7.5 days