Subtraction to 1,000 crossing multiples of ten

General

Students learn to subtract numbers to 1,000 crossing multiples of ten.

Standards

2.NBT.B.7

Learning objective

Students will be able to subtract numbers to 1,000 crossing multiples of ten.

Introduction

Ask students to determine how much further they need to bike. Ask students to explain their strategy as they solve the problems.
Example: The race bike has 460 km to bike. They already biked 250km. How many kilometers does the race bike have left to go?

Instruction

Explain that you can subtract by counting. You first count how many there are in total, this is the first number of the subtraction problem (the minuend). Then you count how many are taken away, which is the second number of the subtraction problem (the subtrahend). When you take the second from the first you are left with the difference. Show this on the interactive whiteboard using the blocks, and discuss the different problems. This includes problems in which the second number (the subtrahend) has hundreds and tens. Check that students are able to solve a few problems on their own or in pairs with the given problems with blocks.Ask them to say the problem they are solving out loud, and to say the steps they are taking out loud. Next explain that you can solve these subtraction problems in different ways. Show that you can use a number line to subtract. You can also split the subtrahend and take away the hundreds and tens in steps. You can also choose to take away the subtrahend in one step. Emphasize to students that they should first carefully look at the problem and then decide which method to use, because all of them work, but some are easier to use on different math problems. Ask students to solve a few problems individually or in pairs, explaining their strategy. Finally walk through the steps of a story problem with the class. Explain that you first determine what kind of math problem it is, then you determine which numbers are important for the problem. You say or write the problem and finally solve the problem. Do one story problem as a class and then ask students to solve another individually or in pairs.

Check that students are able to subtract numbers to 1,000 crossing multiples of ten by asking the following questions:
- What steps do you take to solve a story problem?
- How do you solve 610 - 390?

Quiz

Students are given problems in which they must solve using visual support, solve an abstract problem, and story problems. Encourage students to explain their strategy and walk through the steps of the subtraction problems.

Closing

Discuss with students that it is important to be able to subtract numbers to 1,000 crossing multiples of ten so that you can determine how many you have left. Ask students to solve the problems on the interactive whiteboard. What strategy did they use? Have them explain their work.
To close have students form pairs to work on the problems. The cars each score a goal. Who has the most points left? Example: the blue car has 850 points. When they score a goal they lose 470 points. How many points does the blue car have left? Which car has the most points left after scoring the goals?

Teaching tips

Students who have difficulty with subtraction can be supported by making use of a number line. Show students that they can subtract the numbers in different groups while moving on the number line.