Thank you. K.NBT stands for Kindergarten.Number and Operations in Base Ten. A-CED stands for Algebra-Creating Equations. (Not sure where the D comes in. An example of mixing letters and numbers is 8.NS, which stands for 8th (grade).The Number System. So, we use decimal points when there are numbers and letters, but periods when there are only lettere? Individually cap letters when there are numbers involoved, but double cap when there are only letters?