Start by explaining to students that hundreds numbers always end with zeros in the tens and ones places (00). Then tell students that they can add by counting quantities. Start by counting how many you have, that is the first addend of your addition problem. Next count how many are being added, this is the second addend. When you count the two together, you find the total. Show this on the interactive whiteboard using the blocks and money. Next explain a second type of addition problem. You start by looking to see how many there already are, this is the first addend. Then you look at what the total should be. You then determine how many should be added. You can solve this in different ways. Explain to students that you can add using a number line. You can also turn the addition problem into a subtraction problem. You can also compose the number by adding tens and then hundreds to reach the total. Emphasize that you must look carefully at the addends to determine which method works best for the given problem. Ask students to solve a few problems on their own. Ask them to explain their strategy. Finally show students how to solve a story problem. Show that they must first determine which kind of math problem it is, which numbers are important for the problem, to say or write the problem and finally to solve the problem. Ask students to solve a few story problems individually or in groups.
Check that students are able to add to a hundreds number by asking the following questions:
- What is a useful way to add to a hundreds number?
- How do you solve 385 + _ = 400?