The given arithmetic progression is 8,6,4,2,... When 4 is multiplied to each term of the above arithmetic progression, a new sequence is formed as 32,24,16,8,... Thus the new sequence is also an A.P. with the common difference now as 8. Or, in other words we can say that the new common difference is 4 times the previous common difference. When each term of the A.P. 8,6,4,2,... is divided by 4 we have the new A.P. as 2,1.5,1,0.5,... with the common difference now as 0.5 of the new A.P. Thus the common difference of the previous A.P. gets divided by 4 too.