Mary can do a piece of work in 28 days. Rosy is 40% more efficient than Mary. The number of days taken by Rosy to do the same piece of work is?  Choose the correct answer:
A) 22
B) 24
C) 20
D) 25
E) 27

Rationale: "ratio of times taken by mary and rosy = 140 : 100 = 14 : 10 suppose rosy takes x days to do the work . 14 : 10 : : 28 : x = > x = 20 days . hence , rosy takes 20 days to complete the work . answer : c"
Answer: C