A B and C working in a garment manufacturing company can do the same work assignment in 24 , 6 and 12 days respectively.working together the assignment willbe complete in how many days ?

The best way to solve this is by LCM method
Consider the LCM or any number that is divisible by all three days to be the total work
For example here let's assume 120 to be the total work as it is divisible by 24,6 and 12.
Now if we divide 120 by all these numbers we get the power of abc as 5,20,10 respectively.
To find out the time required by all three we divide 120 by (5+20+10) which is the power of all three.
The time required is 120/35 or 24/7 days
Hope this helps