Ten (chips) = one (strip).
Any number up to 99 can be made by using chips and strips. For each group of ten, you add a strip. For each ones place, you add a chip.
For example: 25 (twenty-five) would be 2 (two) groups of ten and 5 (five) ones.
For example: 79 (seventy-nine) would be 7 (seven) groups of ten and 9 (nine) ones.
Link to Olson home page
Link to Ducheny's home page
Link to Jennifer Nord's little nitch in the woods