Avinash, Bhuvnesh and Chaman can complete a piece of work in 20, 30 and 60 days respectively. In how many days can Avinash complete the work if he is assisted by Bhuvnesh and Chaman on every third day?

Correct option is C

Given:
No of days Avinash takes = 20
No of days Bhuvnesh takes = 30
No of days Chaman takes = 60
Solution:
Avinash, Bhuvnesh and Chaman can complete a piece of work in 20,30 and 60 days
LCM of 20,30,60 =60w (Total work)
Avinash work per day = $$\frac{60}{20}=$$​3w
Bhuvnesh work per day = $$\frac{60}{30}$$​=2w
Chaman work per day =$$\frac{60}{60}$$​=1w
Avinash work every day Bhuvnesh and chaman worked with avinash in every third day so Work done by 3 days=3(3)+3=12w 
then 60 w should be done in  15 days