In this Grade 4 lesson from Pengi Math Chapter 2, students tackle the specific challenge of subtracting across zeros, working through multi-digit problems such as 40,005 minus 12,348 by applying regrouping strategies. Students also learn to verify their subtraction results using addition as an inverse operation, building both accuracy and number sense.
Section 1
Regrouping Across Zeros: The Role of 9s
When regrouping across zeros, the first non-zero digit is reduced by 1, the place value you are regrouping to becomes 10 (or 10 + its original value), and all intermediate zeros become 9. This happens because you are borrowing sequentially. For example:
Section 2
Checking Subtraction with Addition
Addition and subtraction are inverse operations. To check a subtraction problem, add the difference (the answer) to the subtrahend (the number being subtracted). The sum must equal the minuend (the number you started with).
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Section 1
Regrouping Across Zeros: The Role of 9s
When regrouping across zeros, the first non-zero digit is reduced by 1, the place value you are regrouping to becomes 10 (or 10 + its original value), and all intermediate zeros become 9. This happens because you are borrowing sequentially. For example:
Section 2
Checking Subtraction with Addition
Addition and subtraction are inverse operations. To check a subtraction problem, add the difference (the answer) to the subtrahend (the number being subtracted). The sum must equal the minuend (the number you started with).
Book overview
Jump across lessons in the current chapter without opening the full course modal.
Continue this chapter