Bela Abolfathi, D. S. Aguado, Gabriela Aguilar, Carlos Allende Prieto, Andres Almeida, Tonima Tasnim Ananna, Friedrich Anders, Scott F. Anderson, Brett H. Andrews, Borja Anguiano, Alfonso Aragon-Salamanca, Maria Argudo-Fernandez, Eric Armengaud, Metin Ata, Eric Aubourg, Vladimir Avila-Reese, Carles Badenes, Stephen Bailey, Christophe Balland, Kathleen A. Barger, et al (328)
Stair Stringers (7) Stair stringers form the backbone of a set of stairs. By code, stairs need to be at least 36 wide. Although it's usually possible to get away with just using two stringers, we recommend you add a third one down the middle. This extra stringer will ensure your stairs are exceptionally rigid.
As for number of stringers, in my town you would need at least 4 stringers for a 48 inch wide step for an outside stair. This refers to cut stringers, not solid, I just built a set of stairs for my deck, I used cut stringers, 42 inch wide steps, needed four stringers.Each step was 6 inch rise, 12 inch tread. 12 to 1 slope would indeed be very flat, if you go with 6 inch rise per step you are going to need 6 steps for a 42 inch elevation difference, and your stringer would be about 6 feet long if you went with a 12 inch tread.