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Comparing Fractions Using Cross Multiplication

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Basics on the topic Comparing Fractions Using Cross Multiplication

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Cross Multiplication

When we compare fractions, we are determining which one is greater than, less than, or equal to the other.

Cross multiplication is one method used to compare fractions. To compare using cross multiplication: 1)Multiply the denominator of one fraction with the numerator of the other fraction being compared.

2) Compare the products to determine if the fraction is greater than, less than, or equal to the other.

Transcript Comparing Fractions Using Cross Multiplication

Axel and Tank are in the treasure hunt room at the Sunken Ship Funhouse. They get five minutes in the room to find as many treasure chests with the greater amounts of jewels as they can. "This one has two-thirds jewels!" "This one has three-fifths! How do we know which one has more?" In order to collect as many jewels as they can, Axel and Tank will be... Comparing Fractions Using Cross Multiplication. When we compare fractions, we are determining which one is greater than, less than, or equal to the other. Cross multiplication is one method used to compare fractions. To compare using cross multiplication, multiply the denominator of one fraction with the numerator of the other fraction being compared. Then, compare the products to determine if the fraction is greater than, less than, or equal to the other. Let’s use the two-thirds and three-fifths fractions as an example. First, multiply THIS denominator, three, by THIS numerator, three. Three times three is nine. Next, multiply THIS denominator, five, across to THIS numerator, two. Five times two is ten. Now, compare the products. Ten is greater than nine… so two-thirds is GREATER than three-fifths. Why does cross multiplication work when comparing fractions? When we compare fractions with different denominators, we look to make equivalent fractions with the same denominator. We find the least common multiple that each denominator shares and multiplying the numerator by that same number. In the fractions two-thirds and three-fifths, the common denominator is fifteen. Since you multiply three times five to make fifteen, multiply the numerator by five. Two times five is TEN. Five times three is fifteen and three times three equals NINE. Ten-fifteenths is greater than nine-fifteenths...so two-thirds is greater than three-fifths. In cross multiplication, the product of each side of the fraction is the SAME as the numerators created in the equivalent fractions. This method is useful when you are working with fractions with larger numbers or have multiple-step problems to solve. Now, let's help Axel and Tank compare more fractions using cross multiplication. Compare seven-ninths and eight-twelfths. What is nine times eight? Seventy-two. What is twelve times seven? Eighty-four. Is seven-ninths less than, greater than, or equal to eight-twelfths? Seven-ninths is GREATER than eight-twelfths. Compare five-fourteenths and seven-twelfths. Pause the video to solve and press play when you're ready to check the solution. Twelve times five is sixty and fourteen times seven is ninety-eight so, five-fourteenths is LESS than seven-twelfths. Looks like time is running out for Axel and Tank's treasure hunt, so let's review. Remember... when we compare fractions, we are determining which one is greater than, less than, or equal to the other. Cross multiplication is one method used to compare fractions. To solve using cross multiplication, multiply the denominator of one fraction with the numerator of the other fraction across the expression. Then, compare the products to determine which fraction is greater than, less than, or equal to the other. This method is useful when you are working with larger fractions or have a multiple-step problem to solve. "Time's up! How do we get out of here?" "This way!"