Alka can finish a work in 18 days. If Shailja is 20% more efficient than Alka, then in how many days can both of them finish the work together?

Correct option is B

Given:

Alka can finish the work in 18 days.
Shailja is 20% more efficient than Alka. 

Solution: 

Alka   :    Shailji 

100     :    120

5      :        6 

Total time = $$5\times 18 = 90$$ 

They together complete the work = $$\frac{90}{11} = 8\frac{2}{11}$$ days