W and X together can complete a work in 40 days. X and Y together can complete the same work in 60 days. If W, X and Y all work together, then the same work gets completed in 30 days. How many days will W and Y together take to complete the same work?

Correct option is B

Given:
W and X together = 40 days
X and Y together = 60 days
 W, X, and Y together = 30 days
Solution:

Total Work = LCM of 40 , 60 and 30 = 120 unit

Efficiency of W and X together = 3 unit per day
Efficiency of X and Y together = 2unit per day
Efficiency of  W, X, and Y together = 4 unit per day

Efficiency of W = Efficiency of  W, X, and Y  - Efficiency of X and Y 

Efficiency of W = 4- 2 = 2 unit per day.

Efficiency of Y = Efficiency of  W, X, and Y  - Efficiency of W and X

Efficiency of Y= 4- 3 = 1 unit per day.

Time taken by W and Y to complete the whole work = 120 /(2+1) = 120/3 = 40 days