Anshu, Swati and Rajni can finish a work in 4 days if they work together. However, Anshu alone will take 9 days to complete the work, and Swati alone will complete the work in 12 days. How many days will Rajni alone take to complete the work ?

18

Anshu + Swati + Rajni = 4 days

Anshu = 9 days

Swati = 12 days

As, Anshu + Swati + Rajni = 9 

      Anshu = 4

      Swati = 3,

Simplifying it, we get that efficiency of RAJNI is 2.

⇒ Hence, Time taken by Rajni to complete total work alone is = \(\frac{36}{2}\) = 18 days.