New Hampshire Grade 2 Math

Mental addition of ten can change more than one written digit. Place value explains what remains the same and what must be regrouped when the tens reach ten. Compare adding ten with adding one hundred instead of treating both operations as a digit trick.

Try this original activity

Begin with 199. Find 199 + 10 without counting forward by ones. Explain it with hundreds, tens, and ones. Then find 299 + 100 and compare which amount was added. Check the first result by subtracting ten.

Work through the reasoning

The number 199 contains one hundred, nine tens, and nine ones. Adding ten adds one more ten, producing one hundred, ten tens, and nine ones. Ten tens make a hundred, so regroup them to obtain two hundreds, zero tens, and nine ones: 209. The ones stay nine, while both the hundreds and tens digits change. Subtracting ten from 209 gives 199, confirming the result. For 299 + 100, add one hundred to two hundreds, nine tens, and nine ones. The result is three hundreds, nine tens, and nine ones, or 399. These are different additions: ten is one ten, whereas one hundred is ten tens.

Check the common mistake

Writing 1910 appends digits rather than adding a value. Writing 299 for 199 + 10 adds a hundred, not a ten. The shortcut “only the tens digit changes” fails at the boundary in this example. Use a base-ten drawing or bundles when a student gets the correct answer but cannot explain the regrouping. Keep the given starting numbers within the selected standard’s 100–900 range.

Try a related case

Work backward with 200 − 10. Decompose two hundreds as one hundred and ten tens, then remove one ten, leaving one hundred and nine tens: 190. Compare it with 200 − 100 = 100. Ask what was removed in each case and how the result can be checked with addition.

Selected Common Core references for this activity

New Hampshire’s current school-approval rules, Ed 306.34, allow local boards to use the adopted 2010 Common Core mathematics standards or approved alternative academic standards. Confirm the school’s standards choice and local competencies first. The selected Common Core references below were checked in the original publisher’s 2010 document. They identify this activity’s focus, rather than a complete local course. Read the full requirements, mathematical practices, examples, and progression with the school’s curriculum.

Sources checked October 6, 2026. Read complete requirements, clarifications, limitations, and mathematical practices alongside the school’s sequence. This selected activity is an entry point for instruction.

Connect the explanation with practice

Visit the Grade 2 math learning Online Center for broader support or choose a related task from the existing Grade 2 worksheet collection. This is a general collection, not a certification of complete New Hampshire alignment.

Grade 2 is below the Grades 3–8 NH SAS general mathematics range described in the reviewed 2025–2026 public administration manual. Follow the school’s early learning and classroom assessment directions. The reviewed manual is the 2025–2026 edition; confirm later-year directions with the school. Independently published practice may use its own timer, tools, question count, and scoring; these are not official administration specifications or a prediction of a state performance level. Read the public NH SAS manual resource page.

Read New Hampshire local curriculum rules for later guidance. Keep one example of the student’s reasoning with the practice result. Choose a smaller model, a related question, or a new context according to the difficulty revealed in the worked activity.

New Hampshire Grade 2 math: useful study questions