Increasing and Decreasing Evenly In Knitting Patterns

Many knitting patterns will ask you to evenly increase a specific number of stitches over one row. But they won't tell you how often to increase, just to do it evenly.
The basic idea is you don't want your increases all bunched up on one end of the row. You want them spaced as evenly as possible across the row.
The same is true for decreasing evenly. You'll see that direction just as often as increase evenly in a pattern. The principle is the same.
If you're knitting in the round, divide the number of stitches you have at the present time by the number of increases you are to complete. Say you have 100 stitches and the pattern calls for 10 increases evenly across the round. Dividing 100 by 10 equals 10 so you would increase one time every 10th stitch.
If you're knitting back and forth on straight needles,
add one to the number of stitches you are to increase.
Say you have been working 110 sts and you're to increase 10 evenly. Add 1 to 10 which equals 11. Dividing 110 by 11 equals 10 so you would increase one stitch every 10th stitch.
Whether knitting in the round or back and forth, the numbers don't always work out exactly even and you get a fraction instead.
Working back and forth, if you have 120 sts and need to increase 10 (plus add one stitch remember!), divided 120 by 11 and the answer is 10.9. In this case, you would
increase 1 stitch every 10th stitch 9 times and 1 stitch every 11th stitch 1 time if you were knitting back and forth.
Knitting in the round, let's look at increasing 11 sts on a row where you had 100 stitches to begin. Again, that is one stitch every 9.09 stitches. Here, you'd have to cheat again but you would increase 1 stitch every 9th stitch 10 times and 1 stitch every 10th stitch 1 time.
9 x 10 = 90
1 x 10 = 10
Total = 100