Big Ideas Math: Modeling Real Life, Grade 6
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3. Solving Equations Using Multiplication or Division
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Exercise 33 Page 263

b=7.2

Practice makes perfect

To solve the equation, we have to isolate b on one side. Using the Multiplication Property of Equality, we will multiply both sides of the equation by 12. This will eliminate the denominator of the fraction and isolate 7b.

7b÷ 12=4.2
7b/12=4.2
7b/12* 12=4.2* 12
7b=4.2* 12
7b=50.4
7b/7=50.4/7
7/7* b=50.4/7
1* b=7.2
b=7.2

To check that this solution is correct, let's substitute b=7.2 into the original equation and simplify.

7b÷ 12=4.2
7( 7.2)÷ 12? =4.2
50.4÷ 12? =4.2
4.2=4.2 ✓

Since the left-hand side and right-hand side are equal, b=7.2 is the correct solution.

Extra

Properties of Equality
There are four main Properties of Equality that we use when solving linear equations.

Properties of Equality
Addition Property of Equality If a=b, then a+c=b+c.
Subtraction Property of Equality If a=b, then a-c=b-c.
Multiplication Property of Equality If a=b, then ac=bc.
Division Property of Equality If a=b and c is not 0, then a/c=b/c.

In later chapters, you will learn about some more advanced Properties of Equality. As an example, there is a property for when we need to eliminate a radical or an exponent.

Power Property of Equality

If a=b, then a^m=b^m.