Multiplying Whole numbers and Decimals

Today in math we began learning about multiplication. We started with a problem involving rates in which students had to figure out the cheapest store at which to buy dog food. They needed to use their understanding of addition and multiplication to solve these problems. Tomorrow we will extend this problem to 72 cans to see if there is a difference in the cheapest store. Then we will learn a few ways to multiply, both with and without decimals. Here are three common ways to multiply:

1) Break apart method (partial products); 198 x 23

• 8 x 3 = 24
• 90 x 3 = 270
• 100 x 3 = 300
• 8 x 20 = 160
• 90 x 20 = 1800
• 100 x 20 = 2000
• added together 2000 + 1800 + 160 + 300 + 270 + 24 = 4554

2) Lattice multiplication: Click here for video explaining

3) Standard method: Here

I encourage students to use whichever method works for them, but to be aware that there is more than one way to multiply. When they do EQAO, the focus is not so much on being able to multiply, but rather being able to solve problems involving multiplication, including multi-step problems that combine concepts from a variety of strands (eg. number sense and measurement). This is something we will be practicing a lot this year. 

After multiplying, we will be learning how to divide larger numbers, again with or without decimals. I will post later about our process for division.