negative and positive numbers in a sentence

1. There are quite a few'alternative'number representations that have been proposed in the past for making addition and subraction of negative and positive numbers easier where each digit is flagged as either positive or negative rather than the number as a whole.
2. Another keyboard tablature ( though less frequently seen ) is based on a periodic system of numbers, like most modern tablatures, although incorporating negative and positive numbers assigned to the clefs ( as positive for the treble clef and negative for the bass clef ).
3. It's difficult to find negative and positive numbers in a sentence.