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Lesson 6-8: Cross Multiplication

Lesson 6-8: Cross Multiplication. Objective: We will learn to use cross multiplication to solve a proportion. We will use cross multiplication to check whether two ratios form a proportion. Cross multiplication, i n a proportion, is the product of one numerator and the other denominator.

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Lesson 6-8: Cross Multiplication

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  1. Lesson 6-8:Cross Multiplication Objective: We will learn to use cross multiplication to solve a proportion. We will use cross multiplication to check whether two ratios form a proportion.

  2. Cross multiplication, in a proportion, is the product of one numerator and the other denominator. • Property of Cross Products: If two ratios form a proportion, the cross products are equal. If 2 ratios have equal cross products, they form a proportion. • Example 1: • Decide whether each pair of ratios forms a proportion. You have to multiply the numerator with the denominator of the other fraction; and vice versa. 105==105 • 3×35 = 5 ×21 • 105 = 105 If the two products are equal, they form a proportion. When the cross products are not equal, the ratios do not form a proportion. • v

  3. How to Solve a Proportion: For example: 4 = H Steps: 7 84 7×H = 4× 84 1. Write the cross products. 7H = 3362. Multiply 7 H = 336 7 7 3. To find the value of the variable, undo the multiplication by dividing to both sides. H = 48 4. Divide (You have to think: The opposite of multiplication is division, so I have to divide the number that is with the variable and do the same for both sides of the problem. Then I cancel the opposites, and bring down what I have left. ) When solving a proportion you must cross multiply, then find the missing variable.

  4. Your Example: Solve the proportion. 2 = 3 4 N

  5. Homework: • Textbook Pg. 311 #s 7-10 and 15-22. • (Hint: In the first group answer yes or no, but you must show your work. In the second set of problems you must find the value of the variable by cross multiplying. )

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