Standard #: MA.8.NSO.1.2


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Plot, order and compare rational and irrational numbers, represented in various forms.


Clarifications


Clarification 1: Within this benchmark, it is not the expectation to work with the number e.

Clarification 2: Within this benchmark, the expectation is to plot, order and compare square roots and cube roots.

Clarification 3: Within this benchmark, the expectation is to use symbols (<, > or =).



General Information

Subject Area: Mathematics (B.E.S.T.)
Grade: 8
Strand: Number Sense and Operations
Status: State Board Approved

Benchmark Instructional Guide

Connecting Benchmarks/Horizontal Alignment

 

Terms from the K-12 Glossary

  • Irrational Numbers
  • Rational Numbers

 

Vertical Alignment

Previous Benchmarks

Next Benchmarks

 

Purpose and Instructional Strategies

In grade 7, students expressed rational numbers with terminating and repeating decimals. In grade 8, students define irrational numbers, recognizing and expressing them in various forms, and students compare rational numbers to irrational numbers. In Algebra 1, students will perform operations with radicals. In Geometry, students will extend their understanding of radical approximations to weighted averages on a number line. 
  • Students should have the opportunity to draw number lines with appropriate scales to plot the numbers to provide an understanding of where the numbers are in relation to numbers that are greater than and less than the number to be plotted.
  • Students locate and compare rational and irrational numbers on the number line. Additionally, students understand that the value of a square root or a cube root can be approximated between integers.
    • For example, to find an approximation of 28, two methods are described below, each using the nearest perfect squares to the radicand:
      • determine the perfect squares 28 is between, which would be 25 and 36. The square roots of 25 and 36 are 5 and 6, respectively, so we know that 28 is between 5 and 6. Since 28 is closer to 25, an estimate of the square root would be closer to 5.
      • since 28 is located 311 of the distance from 25 to 36, the 28 is approximately located 11 of the distance from 25 to 36. So, this reasoning gives the approximation 25 + 311, which is about 5.27. This method is particularly relevant when students determine weighted averages on a number line in Geometry.
  • Students also recognize that every positive number has both a positive and a negative square root. The negative square root of n is written as −n.
  • Instruction includes the use of technology, including a calculator.

 

Common Misconceptions or Errors

  • Students may not understand that square and cube roots can be plotted on a number line.

 

Strategies to Support Tiered Instruction

  • Instruction includes providing students with examples of square and cube roots for them to place on a number line and facilitating a conversation on understanding the value of each square and cube root.
  • Teacher provides opportunities to co-construct number lines with appropriate scales and plot approximate values of cube roots and square roots.
    • For example, provide partially completed examples of non-perfect square roots and non-perfect cube roots by using perfect square roots and perfect cube roots as benchmark quantities.
  • Teacher provides support in recognizing that every positive number has both a positive and negative square root.
    • For example, show examples of how multiplying two negative numbers gives a positive number, and how the square root of a number can be both positive and negative.
  • Teacher assists students in writing an inequality to represent written statements.
    • For example:
      • Monique has more books than Mary.
      • Mark has 5 pencils and Barry has 8.
      • Animal Kingdom has at least 100 different species of animals.

 

Instructional Tasks

Instructional Task 1 (MTR.6.1)
Below are irrational and rational numbers.

  • Part A. Order the numbers from least to greatest by plotting on a number line.
  • Part B. Identify which numbers are irrational.
  • Part C. Write an inequality that compares a rational number and an irrational number from the list.

 

Instructional Items

Instructional Item 1
Plot −3.42857… on the number line below and explain how you determined its location.
Number line

Instructional Item 2
Using the chart below, compare the irrational and rational numbers shown.
Chart
Chart

Instructional Item 3
Plot the following cube roots on a number line 83, 103 and 273.

 

*The strategies, tasks and items included in the B1G-M are examples and should not be considered comprehensive.


Related Courses

Course Number1111 Course Title222
1200400: Foundational Skills in Mathematics 9-12 (Specifically in versions: 2014 - 2015, 2015 - 2022, 2022 and beyond (current))
1205050: M/J Accelerated Mathematics Grade 7 (Specifically in versions: 2014 - 2015, 2015 - 2020, 2020 - 2022, 2022 and beyond (current))
1205070: M/J Grade 8 Pre-Algebra (Specifically in versions: 2014 - 2015, 2015 - 2022, 2022 and beyond (current))
1204000: M/J Foundational Skills in Mathematics 6-8 (Specifically in versions: 2014 - 2015, 2015 - 2022, 2022 and beyond (current))
7812030: Access M/J Grade 8 Pre-Algebra (Specifically in versions: 2014 - 2015, 2015 - 2018, 2018 - 2019, 2019 - 2022, 2022 and beyond (current))


Related Access Points

Access Point Number Access Point Title
MA.8.NSO.1.AP.2 Use appropriate tools to plot, order, and compare simple square roots and cube roots for quantities less than 100.


Related Resources

Formative Assessments

Name Description
The Irrational Beauty of the Golden Ratio

Students are asked to find and interpret lower and upper bounds of an irrational expression using a calculator.

Approximating Irrational Numbers

Students are asked to plot the square root of eight on three number lines, scaled to progressively more precision.

Locating Irrational Numbers

Students are asked to graph three different irrational numbers on number lines.

Comparing Irrational Numbers

Students are asked to estimate the value of several irrational numbers using a calculator and order them on a number line.

Lesson Plans

Name Description
Testing Imperfection

Students will use number lines to approximate the square root value of non-perfect square numbers to the tenth place. This lesson supports plotting, comparing, and ordering irrational numbers as well as graphing them on a number line, specifically those in the form of nonperfect square roots.

Pin the Irrational "Tail" on the Number Line

Students will use their knowledge of perfect squares and square roots to determine a rational number to approximate an irrational number and find their locations on a number line. They will complete an activity that guides them to zoom further into a number line to find more accurate approximations for irrational numbers. They will conclude that between two rational numbers is another rational number and therefore the further the place value in the approximation, the more accurate the location on the number line.

Rational vs Irrational

Students will organize the set of real numbers and be able to identify when a number is rational or irrational. They will also learn the process of how to change a repeating decimal to its equivalent fraction.

Non-Perfect Square Root Approximations

Students will learn to approximate non-perfect square roots as rational numbers. Understanding that irrational numbers can be approximated by rational numbers can assist students and their understanding of the real number system.

Alas, Poor Pythagoras, I Knew You Well! #2

Using different activities, students will find real life uses for the Pythagorean Theorem.

It's Hip to Be (an Imperfect) Square!

This lesson allows students to explore and estimate the values of imperfect squares, using perfect square anchors and number lines as resources. The conversations throughout the lesson will also emphasize that imperfect squares are irrational numbers that must be estimated to compare.

Problem-Solving Tasks

Name Description
Irrational Numbers on the Number Line

When students plot irrational numbers on the number line, it helps reinforce the idea that they fit into a number system that includes the more familiar integer and rational numbers. This is a good time for teachers to start using the term "real number line" to emphasize the fact that the number system represented by the number line is the real numbers. When students begin to study complex numbers in high school, they will encounter numbers that are not on the real number line (and are, in fact, on a "number plane"). This task could be used for assessment, or if elaborated a bit, could be used in an instructional setting.

Comparing Rational and Irrational Numbers

Students are given a pair of numbers. They are asked to determine which is larger, and then justify their answer. The numbers involved are rational numbers and common irrational numbers, such p and square roots. This task can be used to either build or assess initial understandings related to rational approximations of irrational numbers.

Student Resources

Problem-Solving Tasks

Name Description
Irrational Numbers on the Number Line:

When students plot irrational numbers on the number line, it helps reinforce the idea that they fit into a number system that includes the more familiar integer and rational numbers. This is a good time for teachers to start using the term "real number line" to emphasize the fact that the number system represented by the number line is the real numbers. When students begin to study complex numbers in high school, they will encounter numbers that are not on the real number line (and are, in fact, on a "number plane"). This task could be used for assessment, or if elaborated a bit, could be used in an instructional setting.

Comparing Rational and Irrational Numbers:

Students are given a pair of numbers. They are asked to determine which is larger, and then justify their answer. The numbers involved are rational numbers and common irrational numbers, such p and square roots. This task can be used to either build or assess initial understandings related to rational approximations of irrational numbers.



Parent Resources

Problem-Solving Tasks

Name Description
Irrational Numbers on the Number Line:

When students plot irrational numbers on the number line, it helps reinforce the idea that they fit into a number system that includes the more familiar integer and rational numbers. This is a good time for teachers to start using the term "real number line" to emphasize the fact that the number system represented by the number line is the real numbers. When students begin to study complex numbers in high school, they will encounter numbers that are not on the real number line (and are, in fact, on a "number plane"). This task could be used for assessment, or if elaborated a bit, could be used in an instructional setting.

Comparing Rational and Irrational Numbers:

Students are given a pair of numbers. They are asked to determine which is larger, and then justify their answer. The numbers involved are rational numbers and common irrational numbers, such p and square roots. This task can be used to either build or assess initial understandings related to rational approximations of irrational numbers.



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