To multiply 24 × 3, use the distributive property: break 24 into 20 + 4, then (20 × 3) + (4 × 3) = 60 + 12 = 72. Area models (rectangles divided into tens and ones) support this strategy before introducing the standard vertical algorithm.
You know your multiplication facts up through the nines table, and you've learned the distributive property — that a × (b + c) = (a × b) + (a × c). Two-digit by one-digit multiplication is what happens when you apply that property using place value. Since every two-digit number is built from tens and ones, you can always split it apart in a way that reduces the problem to single-digit facts you already know.
Take 24 × 3. The number 24 is 20 + 4 (two tens and four ones). Applying the distributive property: (20 + 4) × 3 = (20 × 3) + (4 × 3) = 60 + 12 = 72. Each multiplication in the second step is manageable: 4 × 3 = 12 is a basic fact, and 20 × 3 = 60 because 2 tens × 3 = 6 tens = 60. The area model makes this visual: draw a rectangle 24 units wide and 3 units tall, then draw a vertical line separating the 20-unit section from the 4-unit section. The total area equals the sum of the two smaller rectangles' areas.
Once the area model is solid, the standard vertical algorithm you'll use in higher grades is just a compact way to record the same process. When you write 24 × 3 vertically and compute 3 × 4 = 12 (write 2, carry 1), then 3 × 2 = 6 plus 1 carried = 7, you are doing exactly the same steps — just in a streamlined written form. The area model is the picture that makes the algorithm trustworthy; the algorithm is the area model compressed into notation.
The key habit to build is decomposing by place value before multiplying. Any two-digit number splits into tens and ones: 73 × 6 = (70 + 3) × 6 = 420 + 18 = 438. The tens digit always gets multiplied and scaled up by 10. This becomes automatic with practice, and it's exactly the mental process behind multi-digit multiplication of any size.