M.1.1.1

 Understand place value. Understand that the two digits of a two-digit number represent amounts of tens and ones. Understand the following 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, … eight, or nine ones. 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).