Subtraction to 1,000 from hundreds numbers

General

Students learn to subtract numbers to 1,000 from a hundreds number.

Common core standard(s)

2.NBT.B.7

Relevance

It is important to be able to subtract numbers to 1,000 from a hundreds number, so you can determine how much you have left.

Introduction

Ask students to find the difference in the subtraction problems given. Ask students to explain their strategy. You can choose to have students work in pairs or to explain strategy to a partner.

Development

Explain to students that you can subtract by counting amounts. You first count how many there are in total, this is the first number of the subtraction problem (the subtrahend). Then you count how many are taken away, this is the second number of the subtraction problem (the minuend). When you take the second away from the first, you are left with the difference. Show this on the interactive whiteboard using the blocks. Discuss the different subtraction problems, paying particular attention to the fact that the subtrahend (second number) sometimes has hundreds, tens and ones, but does not have to have all of them. Check that students are able to subtract by counting by asking students to take away the blocks shown. Ask them to explain their strategy. Next tell students that you can solve the subtraction problems in different ways. Tell students that you can use a number line to subtract. You can also split the subtrahend into hundreds, tens and ones and take them away from the first number in parts. You can also subtract in one step. Emphasize that students must look carefully at the subtraction problem and then decide which method they like best. Ask students to solve a few problems individually or in pairs and discuss their strategy and the answers as a class. Finally solve a subtraction story problem with the students. Remind students that they must first determine what kind of math problem it is, then to determine which numbers are important, to say or write the math problem, and then to solve the math problem. Solve a story problem as a class and then ask students to solve the next story problem individually or in pairs.

Check that students are able to subtract numbers to 1,000 from hundreds numbers by asking the following questions:
- What steps do you take to solve a story problem?
- How do you solve 500 - 268?

Guided practice

Students are given subtraction problems with visual support, in the abstract, and subtraction story problems. They are asked to select from multiple choice answers as well as fill in the missing answer.

Closing

Discuss the importance of the learning goal with the students, and that when you are able to subtract numbers to 1,000 from a hundreds number, they'll be able to find the difference on their own. Ask students to solve the problems on the interactive whiteboard. Ask students to explain their strategy. How did they solve the problems? To close the lesson ask students to form pairs. A number has fallen down the stairs and at every step they lose some numbers. Ask the pairs to determine how much is left when the number reachers the bottom of the stairs. Discuss the answers as a class.

Teaching tips

Students who have difficulty with subtraction can be supported by the use of a number line during subtraction. Remind students that they can take jumps of different sizes (hundreds, tens, fives, twos, ones, etc.)