Welcome to "Muffin Sale Tracker", a 2nd Grade Subtraction mission at the Explorer (core) level, staged in our bakery scenario. The mission opens with a hands-on prompt: "You have 91 muffins, bundled as 9 ten-bundles and 1 loose one. Build that starting amount." You'll work with the numbers 91, 9, 1 and arrive at a final answer of 91 across 3 guided steps.
Behind the bakery story, this lesson is really about subtraction aligned to CCSS 2.NBT.B.5. Fluently subtract within 100, including regrouping (borrowing) across the tens–ones boundary. The key strategy this mission asks you to internalise: 91 − 46 = ?
A general pattern to watch for in 2nd Grade subtraction — illustrated with example numbers below, which may differ from this lesson's: Subtracting the smaller ones digit from the bigger one regardless of position (52 − 26 → 34). The top number is the one we're taking *from*. If it is too small in a column, we must un-bundle — never swap. If you get stuck on "Muffin Sale Tracker", the adaptive Socratic hints below escalate from a gentle nudge to a worked-out strategy — the same way a one-on-one tutor would coach you through it.
Grade 2 · Subtraction
Mission Progress
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Thinking Summary · 1
Mastered[object Object]
[Discovery] You have 91 muffins, bundled as 9 ten-bundles and 1 loose one. Build that starting amount.
1
Active StepDistribute items equally among groups
Everything you need to know about the Socratic experience.
You have 91 muffins, bundled as 9 ten-bundles and 1 loose one. Build that starting amount. Hint: Add 9 groups of 10, then 1 more group with only 1.
Check by adding: does 45 + 46 equal 91? If you get stuck, the adaptive hint is: One fact-family: 46 + 45 = 91, 91 − 46 = 45, 91 − 45 = 46.
Explorer missions hit the core abstraction at typical numeric ranges — this is where conceptual mastery is built. Within 2nd Grade Subtraction, expect numbers in the corresponding range.
Forgetting to lower the tens digit after borrowing. When you un-bundle one ten, the tens column loses 1. Write the new smaller tens digit on top before continuing.
Addition (Inverse partner — checking a subtraction with addition locks in fluency.). Open /grade-2/addition 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.
C-P-A is the Singapore Math sequence proven to deepen number sense: first manipulate physical objects (Concrete), then draw pictures of them (Pictorial), and only then write equations (Abstract). Inquiry AI structures every mission as exactly these three steps — a manipulative, a picture/grid model, and finally the equation. Skipping straight to symbols is the #1 cause of math anxiety; the platform refuses to do it.
