Sakshi can do a piece of work in 20 days. Tanya is 25% more efficient than Sakshi. The number of days taken by Tanya to do the same piece of work is:

A.    15   
B.    16
C.    18   
D.    25
Answer: B

Explanation:

Ratio of times taken by Sakshi and Tanya = 125 : 100 = 5 : 4.
Suppose Tanya takes x days to do the work.
5 : 4 :: 20 : x  =>  x = (4 x 20/ 5)
                           x = 16 days.
Hence, Tanya takes 16 days to complete the work.