Mean=total/the number of values =>total=mean*the number of values the total of the first set of 8 numbers is : total=8*8=64 the total of the second set of 12 numbers is: 12m the total of the 20 numbers is: 64+12m the mean of the 20 number is: (64+12m)/20=5 solve for m: 64+12m=100 12m=36 m=3