1.NBT.B.2 - Understand that the two digits of a two-digit number represent amounts of tens and ones. Understand the following as special cases:

1.NBT.B.2b - Understand that the two digits of a two-digit number represent amounts of tens and ones. The numbers from 11 to 19 are composed of a ten and one, two, three, four, five, six, seven, eight, or nine ones.