First shaping "follow 1 alt rows"?

How-to Questions
1

Hello, making first garment with shaping, a child vest. Two questions actually.

Dec on next 3 rows and on following 1(2:3) alt rows.

I am making smallest size so after decreases on 3 rows, am I to decrease on the 4th row or skip one row and decrease on row 5?
Which row is the following 1 alt row?

Also, garment started with 6 rows of ribbing [working bottom up]. If back is worked “continue in pattern until back measures xx inches” am I to include the ribbing in the measurement or only measure the pattern stitch that makes up the body.

Thanks in advance!

2

These instructions would mean dec on 3 row, work 1 row plain, then dec the next row.

To `continue until back measures xx inches’ means the whole back from the cast on.

sue

3

Many thanks, now I can go on! mk