Learn · Illustrative Mathematics K–5 · Grade 3 · Unit 3
Short lessons you can play with. Build numbers from hundreds, tens, and ones, add and subtract on open number lines and by place, use the standard algorithms, round to the nearest ten and hundred, estimate to check an answer, and solve stories with two steps, then check yourself.
Nine short chapters follow the unit’s lessons in order. Each step shows one idea with something to tap or move, then a quick check. A wrong answer names the likely mistake and gives one more try. Progress is saved on this device.
Every number stays within 1,000. Problems regroup in the ones, the tens, or both, and some subtract across a zero, as the unit’s algorithm lessons do. Rounding is to the nearest ten or hundred, and a number exactly halfway rounds up.
Expanded form: a number written as what its digits are worth, 346 = 300 + 40 + 6. Open number line: a line for jumping on or back, not drawn to scale. Regroup: trade 10 of one place for 1 of the next (or 1 for 10), to add or subtract by place. Algorithm: a set of steps that always works, like adding by place from the ones. Round: find the nearest ten or hundred. Estimate: an answer close to the exact one, found with friendly numbers.
Classroom Supplies (Lesson 21) is an optional lesson. Practice it all in Treasure Cove, the game for this unit.