Answer :
2/12+4/12+1/12= 7/12, 12-7 = 5, so 5/12 participate in the volunteer programs.
It will be 5/12 because, if you add 2+4+1=7/12 and that is not a hole number so you add as many that will make it a hole number so I just added 5 to get 12/12 a hole number.