Mary can do a piece of work in 11 days. Rosy is 10% more efficient than Mary. The number of days taken by Rosy to do the same piece of work is? Select:
A) 10  B) 15  C) 20  D) 25  E) 30

Rationale: "ratio of times taken by mary and rosy = 110 : 100 = 11 : 10 suppose rosy takes x days to do the work . 11 : 10 : : 11 : x = > x = 10 days . hence , rosy takes 10 days to complete the work . answer : a"
Answer: A