Today we are going to learn how to multiply by 2-digit numbers. If you know to multiply by 1-digit numbers, this will be a piece of cake. You just need to follow a few steps, it’s easy.
Let’s review some examples.
Example 1: multiply 53 × 42
First, write one number above the other, so the ones’ and tens’ places are lined up. Next, multiply 53 by 2 ones. Continue multiplying 53 by 4 tens or 40. Finally, add the two partial products to get the answer. Take a look at the image below:
We get a final answer of 2 226.
Example 2: multiply 154 × 23
First, write one number above the other, so the ones’ and tens’ places are lined up. Next, multiply 154 by 3 ones. Continue multiplying 217 by 2 tens or 20. Finally, add the two partial products to get the answer.
The final answer is 3 542.
Example 3: multiply 217 × 35
First, write one number above the other, so the ones’ and tens’ places are lined up. Next, multiply 217 by 5 ones. Continue multiplying 217 by 3 tens or 30. Finally, add the two partial products to get the answer.
The final answer for this problem is 7 595.
The language of algebra
Don’t forget that in a multiplication, the numbers that are being multiplied are called factors. In the last example, the numbers 1 085 and 6 510 are called partial products, and we add them to get the product. Take a look at the image below:
Video
In the following video, we will take a look at other examples.
References
For this article, we used these references:
- Dorling Kindersley Limited (2016). How to be good at math (pp. 120-121).
- Tussy, K., Gustafson, D. y Koenig, D. (2013). Prealgebra (4° ed.; pp. 36-38). Cengage Learning.
- OpenStax (2020). Prealgebra 2e (pp. 61-63). Rice University.