Presentation on theme: "Lesson 6-8: Cross Multiplication"— Presentation transcript:
1Lesson 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.
2Property of Cross Products: 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 theother fraction; and vice versa.105 = =1053×35 = 5 ×21105 = 105If the two products are equal, they form a proportion.When the cross products are not equal, the ratios do not form a proportion.v
3How to Solve a Proportion: When solving a proportion you must cross multiply, then find the missing variable.For example: = H Steps:7×H = 4× 841. Write the cross products.7H = Multiply7 H = 336To find the value of the variable, undo themultiplication by dividing to both sides.H = 484. 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. )
5Homework: 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. )