1.NBT.2a - Understand place value

Understand that the two digits of a two-digit number represent amounts of tens and ones. Understand the following as special cases:10 can be thought of as a bundle of ten ones — called a “ten.”

CC.1.NBT.2 Understand place value. Understand that the two digits of a two-digit number represent amounts of tens and ones. Understand the following as special cases:
-- a. 10 can be thought of as a bundle of ten ones — called a “ten.”
-- b. The numbers from 11 to 19 are composed of a ten and one, two, three, four, five, six, seven, eight, or nine ones.
-- c. The numbers 10, 20, 30, 40, 50, 60, 70, 80, 90 refer to one, two, three, four, five, six, seven, eight, or nine tens (and 0 ones).