Fourth Grade Math Lessons on Negative Numbers
The concept of negative numbers is abstract and therefore relatively difficult for some fourth-grade students to understand. The combination of real-world application as well as group discussion and rote practice helps children with different learning styles master the concepts. Using lesson plans that incorporate multiple intelligences ensures that students retain the information for years to come.
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Introduction to Opposites
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Start with the concept of "opposites," a concept that fourth graders are familiar with. Ask them to raise their hands and come up with a list of three or four opposites; write them on the board.
Now ask: What is the opposite of positive? The answer is negative. And there are positive and negative numbers.
Addition
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Assure the children that you know that if there are three apples on the table, you cannot subtract five apples. However, there are times in life when you can count below zero, and when you do so you are using negative numbers.
Temperature is a real-life example in which we use negative numbers. Ask them, can it get colder than 0 degrees? Of course it can! Now ask, which is colder, negative 5 degrees or negative 12 degrees?
Draw two number lines on the board, one horizontal and one vertical. Fill in from -12 to +12. When discussing temperature, use the vertical number line.
Abstract concepts, such as keeping points in a game, may use negative numbers. Use the horizontal number line to show things like 2 + -7 and other addition equations using negative numbers.
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Subtraction
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After practicing with addition as a group, move on to the concept of subtraction. Ask: What do you think happens if you take away something negative? Go back to the thermometer or vertical number line. Let's say it is -7 degrees outside. If we add -3 degrees, that means it is getting colder.
-7 + -3 = -10.
So, if we "take away" -3 degrees, that is the opposite of adding. The opposite of getting colder is getting warmer, so subtracting -3 is just like adding 3.
-7 - -3 = -4.
Write the equations on the board so the class can see you turn the minus sign and the negative sign before 3 into plus signs. Repeat the mantra: "Minus negative equals plus positive." Some of your students will hear the mantra repeated and remember it, others will need to see it on the board, and still others will need the temperature example to learn the concept of negative numbers.
Multiplication and Division
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Multiplication and division of negative numbers may be taught after the class has mastered addition and subtraction of negative numbers. Remind the class that positive and negative are opposites, addition and subtraction are opposites, and multiplication and division are opposites.
Ask: When you multiply two positive numbers, what is the result? Answer is positive. When you multiply two negative numbers, what is the result? The students will be surprised that the answer is positive. Write on the board:
+ x + = +
- x - = +
So, multiplying by the same gives a positive result.
+ x - = -
- x + = -
So, multiplying by the opposite gives a negative result.
The same rules apply to division:
+ / + = +
- / - = +
and
+ / - = -
- /+ = -
Practice examples together on the board and give students the chance to solve the problems on the board. Once they seem to get the hang of it, move on to the card game.
Card Game
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Use a regular deck of playing cards. Black numbers are positive, red numbers are negative. Remove Aces and face cards from the deck. Hold up two cards and call out either "addition, subtraction, multiplication or division." Allow the students to raise their hands to solve the problem. They must also tell why the answer is the right answer. Allow students to discuss the math problems and help each other solve them during this game.
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References
- Photo Credit numbers image by dip from Fotolia.com
