Explanation:

Correct option:3

Given that A and B together can complete a piece of work in 40 days, B and C can do it in 60 days and C and A can do it in 30 days.

We know that efficiency=total work / time taken to complete the work

So the total work=LCM(40,60,30)=120units
Efficiency of A+B=120/40=3 unit/day
Efficiency of B+C=120/60=2 unit/day
Efficiency of C+A=120/30=4 unit/day
Efficiency of A+B+C=9/2=4.5 unit/day

Totatal time taken by A,B and C to complete the work=total work/efficiency of A,B,C

=>120/4.5=80/3 days

A, B, and C together can complete half of the actual work =( 80/3 ) / 2=40/3 days