Multiplying by 1-Digit Numbers

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Concept Review

Multiplying by 1-Digit Numbers: The Power of Groups

Imagine you're organizing a school pizza party. Each table seats 24 students, and you need to set up 3 tables. How many students can you seat in total? This is where multiplying 2-digit numbers by 1-digit numbers becomes your superpower!

When we multiply a 2-digit number by a 1-digit number, we're essentially asking: "How many are in this many equal groups?" Let's solve our pizza party problem step by step.

Breaking It Down: The Place Value Method

To multiply 24 × 3, we can split the 2-digit number into its place value parts:

24 × 3 = ?

Step 1: Break apart 24 → 20 + 4

Step 2: Multiply each part by 3

• 20 × 3 = 60

• 4 × 3 = 12

Step 3: Add the results → 60 + 12 = 72 students

The Standard Algorithm

We can also solve this using the traditional multiplication method, working from right to left:

× 3

12 ← (4 × 3)

+ 60 ← (20 × 3)

🔥 The Regrouping Secret

Here's the cool part: when you multiply the ones place and get more than 9, you "carry" or regroup!

Try 47 × 2. When you multiply 7 × 2 = 14, you write down the 4 and carry the 1 ten over to help with 4 × 2. So: 4 × 2 = 8, plus the carried 1 = 9. Answer: 94!

Why This Works

This method works because of the distributive property—we can multiply each part separately and then combine. Whether you're calculating 15 × 4 (like buying 4 packs of 15 stickers), 38 × 6 (finding the total pages in 6 books of 38 pages each), or 73 × 8, the process stays the same: break apart, multiply, and combine.

🔑 Key Takeaway

Just like setting up those pizza tables, multiplying 2-digit by 1-digit numbers helps us quickly find totals when we have equal groups. Whether it's 24 students per table or 47 pencils per box, multiplication gives us the power to organize and count our world efficiently!

Sample questions

1. Solve: 43 × 6

✓ 258

○ 248

○ 243

○ 253

Answer: 258 — 6 × 3 = 18 (write 8, carry 1). 6 × 4 = 24. 24 + 1 = 25. Result: 258.

2. What is 87 × 4?

○ 328

✓ 348

○ 368

○ 347

Answer: 348 — 4 × 7 = 28 (carry 2). 4 × 8 = 32. 32 + 2 = 34.

3. Calculate 59 × 3.

○ 157

○ 167

✓ 177

○ 187

Answer: 177 — 3 × 9 = 27 (carry 2). 3 × 5 = 15. 15 + 2 = 17.

Skills in this topic

Multiply a 2-digit number by a 1-digit number
Multiply a 3-digit number by a 1-digit number
Multiply a 4-digit number by a 1-digit number
Identify errors in a multiplication calculation
Solve real-world word problems multiplying by 1-digit numbers

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