Mathematics
Grade 9
15 min
Compare fractions using benchmarks
Compare fractions using benchmarks
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1
Introduction & Learning Objectives
Learning Objectives
Identify and use the key benchmarks of 0, 1/2, and 1 to compare fractions.
Determine if a fraction is less than, equal to, or greater than 1/2 by comparing the numerator to half of the denominator.
Determine if a fraction is less than, equal to, or greater than 1 by comparing the numerator to the denominator.
Compare two fractions by analyzing their relative positions to a common benchmark.
Reason about the 'distance' of a fraction from a benchmark to compare two fractions on the same side of that benchmark.
Apply benchmark reasoning to evaluate the magnitude of simple rational expressions for a given value of the variable.
You have 7/8 of a pizza left, and your friend has 8/10 of a pizza left. Without doing complex math, who has more? 🍕
This...
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Key Concepts & Vocabulary
TermDefinitionExample
Benchmark FractionA common, easy-to-visualize fraction (like 0, 1/2, or 1) that we use as a reference point to compare other, more complex fractions.To compare 4/9 and 5/8, we can use the benchmark of 1/2. We see that 4/9 is less than 1/2, and 5/8 is greater than 1/2.
NumeratorThe top number in a fraction. It represents how many parts of the whole you have.In the fraction 3/5, the numerator is 3.
DenominatorThe bottom number in a fraction. It represents the total number of equal parts the whole is divided into.In the fraction 3/5, the denominator is 5.
Rational ExpressionAn expression that is the ratio of two polynomials, essentially a fraction containing variables.(x + 2) / (x - 3). Comparing fractions is a foundational skill for estimating the value of these expres...
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Core Formulas
Comparing to the Benchmark 1
For a positive fraction \( \frac{a}{b} \): If \( a < b \), then \( \frac{a}{b} < 1 \). If \( a = b \), then \( \frac{a}{b} = 1 \). If \( a > b \), then \( \frac{a}{b} > 1 \).
Use this rule to quickly determine if a fraction's value is less than, equal to, or greater than one whole by simply comparing the numerator and the denominator.
Comparing to the Benchmark 1/2
For a positive fraction \( \frac{a}{b} \): If \( 2a < b \), then \( \frac{a}{b} < \frac{1}{2} \). If \( 2a = b \), then \( \frac{a}{b} = \frac{1}{2} \). If \( 2a > b \), then \( \frac{a}{b} > \frac{1}{2} \).
Use this rule to determine if a fraction is less than, equal to, or greater than one-half. This is equivalent to checking if the numerator is less than...
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Challenging
For which positive integer values of x is the rational expression (x+4)/(3x+3) greater than 1/2?
A.x < 5
B.x > 5
C.All positive integers
D.No positive integers
Challenging
You are comparing two fractions, a/b and c/d. Both are greater than 1/2 but less than 1. You find that 1 - a/b = 1/n and 1 - c/d = 1/(n+1) for some positive integer n. Which statement must be true?
A.a/b > c/d
B.a/b < c/d
C.a/b = c/d
D.More information is needed.
Challenging
Which fraction lies on a number line between 12/13 and 14/15?
A.11/12
B.15/16
C.16/17
D.13/14
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