1.NBT.2 Unerstand that the 2 digitds of a 2 digit numberr represent amounts of tens ones. Understand the following as special cases: 1.) 10 can be thought of as a bundle of ten ones. 2.) The numbers 11 - 19 are compsed of a ten and one, two, three, four, etc.. ones. 3.) The numbers 10, 20, 30, etc... refer to 1, 2, 3, etc. tens and zero ones. I would use this as a partner math center after having introduced and done it whole group.