Welcome to "Crew Roster Math", a Grade 2 Add and Subtract within 100 mission at the Seedling warm-up level, staged in a space scenario. The mission opens with a hands-on prompt: "We will subtract 27 and 13. First, model the tens of 13: build 1 pods of 10 rations." Students work with the numbers 27, 13, 1 and reach a final answer of 27 across 3 guided steps.
Behind the story, this lesson builds add and subtract within 100 understanding aligned to CCSS 2.NBT.B.5. The key strategy is: 27 − 13 = 14.
A common misconception this page surfaces is: Subtracting digit-wise smaller-from-larger (32 − 15 → doing 5−2 then 3−1 = 23). When ones can't subtract, borrow from tens. Subtraction always goes top minus bottom, even if you must regroup first. The adaptive Socratic hints move from a small nudge to a fuller strategy, keeping the reasoning visible for students, parents, and teachers.
Grade 2 · Add and Subtract within 100
Mission Progress
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Thinking Summary · 1
Mastered[object Object]
[Discovery] We will subtract 27 and 13. First, model the tens of 13: build 1 pods of 10 rations.
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Active StepDistribute items equally among groups
Everything you need to know about the Socratic experience.
We will subtract 27 and 13. First, model the tens of 13: build 1 pods of 10 rations. Hint: 13 = 1 tens + 3 ones. We're building only the tens portion now.
If 27 − 13 = 14, then 14 + 13 = ? If you get stuck, the adaptive hint is: Inverse of "− 13" is "+ 13". So the answer is 27.
Seedling missions anchor the visual model with small, friendly numbers — ideal as the first attempt at this topic. Within Grade 2 Add and Subtract within 100, expect numbers in the corresponding range.
Subtracting digit-wise smaller-from-larger (32 − 15 → doing 5−2 then 3−1 = 23). When ones can't subtract, borrow from tens. Subtraction always goes top minus bottom, even if you must regroup first.
Number Line Add/Sub (A second representation of the same operations.) Open /grade-2/numberlinejump to start that topic's missions.
Yes. Every mission, handbook page, and topic hub is mapped to a specific CCSS code (visible in the page header). The curriculum follows the CCSS coherence map: Grade 1 number sense → Grade 3 multiplicative thinking → Grade 6 ratio reasoning, with each grade building strictly on the prior year's foundations.
Inquiry-based learning starts with a question, not a formula — students explore, hypothesize, and verify before being told the rule. In Inquiry AI, every mission opens with a "Discovery" step (manipulate the model), then "Abstraction" (write the equation), then "Reflect" (apply to a new case). The procedure is never given upfront; learners derive it from their own observations.
