Making sense of my pattern?

[Cardamin]

My grandma used to knit me a pair of mittens every year for Christmas and I loved them all. After she died, I received all of her knitting needles and yarn, and greatly wished that I had asked her to teach me some basic knitting skills while she was still able - I guess I was too young to even think of it. Finally I decided I was going to take matters into my own hands and teach myself - wow, was it ever hard! Being a leftie, learning everything right-handed made things very frustrating for a while, but I think I have figured out enough to move on from the rectangles I have been making.
Anyway, I found a pattern for mittens that seemed fairly straightforward, and I've made it through the cuff and the next few rows with no hitches, but I seem to be stuck and was hoping somebody would be able to set me straight.

The pattern is here: http://www.freevintageknitting.com/mittens/104-mittens-pattern.html

I'm working on the pair for 10-year olds, with 38 stitches cast on.
When it comes to the thumb increases, the first increase says to knit 18, inc. 1 st, k 1, inc. 1 st, k 17 sts.
But if I have 38 stitches, and am adding 2, shouldn't that add up to 40? I can only see 38 accounted for in those instructions. Am I reading this wrong? Any clarification would be awesome! Thank you!

[suzeeq]

I think the inc is a kfb which would use up the other 2 sts. 18+17=35, plus k1=36, plus kfb, kfb = 40. If you used a M1 inc it adds a st between sts and you'd only need 36 sts.

[Cardamin]

Thanks so much for such a fast response! That makes a lot of sense, although I'm not sure I would have ever figured it out myself!

[suzeeq]

When a pattern calls for an increase, however they word it, and the numbers don't work out when you try it, use a different increase.

[imrachel]

Here is what they're having you do:

K18, increase in the next st (which, as suzeeq said, is a KFB), K1, increase in the next st, K17. So it's 18 + 1 + 1 + 1 + 17 = 38. If you don't like the way the KFB looks (it tends to leave a little hole, whereas the increase where you pull up the yarn from the row below doesn't), then you can do it this way: K19, M1, K1, M1, K18.

[OffJumpsJack]

I think the inc is a kfb which would use up the other 2 sts. 18+17=35, plus k1=36, plus kfb, kfb = 40. If you used a M1 inc it adds a st between sts and you'd only need 36 sts.

Perhaps I can tag along here?

If a KFB can leave a little hole, then can you twist the stitch before you KFB to close up the hole? I thought I read somewhere about twisting a YO to close it up a bit, so thought it might work with a KFB.

(Now I just need to find Amy's vid on KFB again. I forgot how to do a KFB.) :doh:

[suzeeq]

I've never found that kfb leaves a hole though it might if you do it tight, so keep it looser and the yarn fills it in. The kfb is twisted in a sense anyway; you knit into the front loop, then when you knit into the back loop, that original st is twisted around.