Skill: Subtract a 1-digit number from a 2-digit number with regrouping

Explanation and Free Practice Resources

This understanding involves decomposing a two-digit minuend by exchanging one ten for ten ones when its ones digit is less than the one-digit subtrahend, then finding the difference while preserving the quantity. Place-value drawings, equations, and number lines can show that the regrouped number is equivalent to the original and help prevent treating the tens and ones digits as independent; this reasoning supports subtraction with larger numbers.

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Detailed Explanation: Subtract a 1-digit number from a 2-digit number with regrouping

When the ones digit is smaller than the number you are subtracting, regroup one ten as ten ones.

Example: subtract $7$ from $42$ .

Write the numbers by place value:
- $42$ has $4$ tens and $2$ ones.
- We cannot subtract $7$ ones from $2$ ones.
Exchange $1$ ten for $10$ ones:
- $4$ tens becomes $3$ tens.
- $2$ ones becomes $12$ ones.
The amount is still the same because

42=3\text{ tens}+12\text{ ones}=30+12.

Subtract the ones:

12-7=5

Subtract the remaining tens:

3\text{ tens}=30

Put the tens and ones together:

30+5=35

So,

42-7=35.

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Subtraction - Whole Number 2 x 1, With Borrow

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Units Teaching This Skill

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