2.NBT.B.9 Grade 2 · Number and Operations in Base TenExplain why addition and subtraction strategies work, using place value and the properties of operations.10Common Core State Standards for Mathematics, as adopted in the Massachusetts Curriculum Framework for Mathematics (2017), Grade 2.
Play the game: Which Way?Step 33 of the ColorMyMath curriculum · free, no sign-up →Past nine, color tells you which place a digit lives in. A ten is a triangle of ten dots; the number of triangles is the tens digit, so 34 is three triangles and four loose green dots.
Every page is free and open — nothing to install, no account, and it works on a phone or a classroom board. Every number has its own color: 1 red, 2 orange, 3 yellow, 4 green, 5 blue, 6 purple, 7 brown, 8 pink, 9 cyan, and a number is that many colored dots.
Step 33Proving doubles subtraction: Trampoline Jump Down, or Climb to Ledge then SummitStep 53Two-digit addition with hard facts — carryingStep 55Two-digit subtraction with hard facts — borrowingStep 58Complements of 100: 55+45, 65+35, 75+25, 85+152.NBT.A.1Hundreds, tens and ones in a three-digit number2.NBT.A.2Count within 1000; skip-count by 5s, 10s and 100s2.NBT.A.3Read and write three-digit numbers: numerals, words, expanded form2.NBT.A.4Compare three-digit numbers with >, = and <2.NBT.B.5Add and subtract within 100 fluently using place value2.NBT.B.6Add up to four two-digit numbers: gather the tens first, then the ones2.NBT.B.7Add and subtract within 1000; sometimes tens or hundreds are made or broken2.NBT.B.8Add or take 10 or 100 from a number between 100 and 900 in your headColorMyMath · getridoftheteacher.com · every number has its own color, and a number is that many colored dots. Matching a game to a standard is a judgement call; the official text is at doe.mass.edu.