**A, B and C can do a piece of work in 12, 15 and 20 days respectively. How long will they take to do it working together ?**

###### Answers:

A can do a piece of work in 12 days

B can do the same work in 15 days

C can do the same work in 20 days

∴ A’s 1 day’s work = 1/12

B’s 1 day’s work = 1/15

C’s 1 day’s work = 1/20

∴ (A + B + C)’s together 1 day’s work = 1/12 + 1/15 + 1/20

= (5 + 4 + 3)/60

= 12/60

= 1/5

∴ They can do the work in 5 days.