Skill: Multiply a 2-digit number by a 1-digit number

Explanation and Free Practice Resources

Multiplying a two-digit whole number by a one-digit whole number involves decomposing the two-digit factor into tens and ones, finding the corresponding partial products, and combining them using place value and the distributive property. An area model, array, or equations such as $24 \times 3=(20\times3)+(4\times3)$ connects these quantities to the standard algorithm, including regrouping when the ones product is 10 or more; larger factors and more advanced generalizations are not included.

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Detailed Explanation: Multiply a 2-digit number by a 1-digit number

To multiply a 2-digit number by a 1-digit number, break the 2-digit number into tens and ones. Multiply each part, then add the partial products.

Example: Find $27 \times 4$ .

Break apart 27:

27=20+7

Multiply each part by 4:

20\times4=80

7\times4=28

Add the partial products:

80+28=108

So,

27\times4=108

Using the standard algorithm, multiply the ones first:

$4\times7=28$ . Write $8$ ones and regroup $2$ tens.
$4\times2=8$ tens, plus the $2$ regrouped tens gives $10$ tens.

That is $100+8=108$ .

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Multiplication Area Model - Twenties to Total

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