Lesson 4

Multi-digit Multiplication

Multiply larger numbers using the area model and the standard algorithm

The area model

The area model breaks multiplication into smaller, friendlier pieces.

Example: 23 × 14

104 203 20 × 10 = 200 20 × 4 = 80 3 × 10 = 30 3 × 4 = 12 200 + 80 + 30 + 12 = 322

Split each number by place value and multiply each pair. Then add all four parts: 200 + 80 + 30 + 12 = 322

This works because 23 × 14 = (20 + 3) × (10 + 4) — the distributive property!

The standard algorithm

Once you’re comfortable with the area model, the standard algorithm is faster:

    2 3
  ×  1 4
  -----
    9 2   ← 23 × 4
  2 3 0   ← 23 × 10
  -----
  3 2 2

Steps:

  1. Multiply 23 by the ones digit (4): 23 × 4 = 92
  2. Multiply 23 by the tens digit (10): 23 × 10 = 230
  3. Add the partial products: 92 + 230 = 322

Step 1: Ones

Multiply 23 by the ones digit (4): 23 × 4 = 92. Write 92 as the first partial product.

Step 2: Tens

Multiply 23 by the tens digit (10): 23 × 10 = 230. Write 230 as the second partial product.

Step 3: Add

Add the partial products: 92 + 230 = 322. That's 23 × 14!
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23
14

Tips for carrying

When a column product is 10 or more, carry the tens digit:

Example: 47 × 6


Practice

Use any method: 36 × 12 = ?

Calculate 54 × 23.

Which area-model partial product is missing? 45 × 27: (40×20) + (40×7) + (5×20) + ?

A cinema has 28 rows with 32 seats in each row. How many seats total?

seats

When multiplying 63 × 8, you get 6 × 8 = 48 in the tens column. What do you carry?

Challenge

Quick-Fire Round

Score: 0 / 6 Problem 1 of 6