Clarification help please

[DavidSydney63]

OK - so I'm working a vee-neck jumper (sweater).

On the back I've worked the desired number of rows so that 41cms is achieved.

Now - the pattern says:

Work 20 rows in stripes of 10 rows C, 6 rows M and 4 rows C, AT THE SAME TIME dec one st at each end of next row, then in every foll alt row 6 times ... 104 sts.

OK - so the colour changes are basic enough - I understand that perfectly. As this procedure begins on the right side in stocking stitch (a knit row). Am I to assume that the decreases talking about are on purl rows? - wisdom sought.