Pattern Reading

[-Kenny-]

Hi! Im new to crocheting and I'm reading a pattern my mom got me for Christmas and i understood most all of it until this point when is says "Sc1, hdc 1, sc 1 in one st, sc 1 in next st,* 21 times." I'm starting with 42 stitches around my circle and i should end up with 84. does sc 1 in on st , mean on stitch after the hdc(half double stitch) and the and then another time ? 

[bgs]

Sc1, hdc 1, sc 1 in one st, sc 1 in next st,* 21 times." 

You are going to be putting 3 stitches into one stitch. 

sc, hdc, and a sc all go into one stitch of the previous round.  Then you sc in next stitch.  You repeat this entire sequence 21 times. 

4 stitches× 21=84 made

2 stitches used in previous round ×21 =42 stitches used 

[-Kenny-]

Oh that makes a lot more sense! Thank you so much