Envision Math 2.0: Grade 8, Volume 1
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2. Understand Irrational Numbers
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Exercise 6 Page 16

A rational number can be written as the ratio of two integers. Conversely, an irrational number cannot be written as the ratio of two integers.

Rational Irrational
4.27 0.232342345...
0.375 sqrt(62)
- 13/1
Practice makes perfect

We will classify the given numbers as a rational or an irrational number and fill the table. To do so, let's first recall the definitions of rational numbers and irrational numbers.

  • Rational Numbers: Numbers that can be expressed as the ratio of two integers.
  • Irrational Numbers: Numbers that cannot be expressed as the ratio of two integers.
With these definitions in mind, let's now consider the given numbers one by one.

Classify 4.27

Note that the symbol on top of the digit 7 means that this number is repeated indefinitely. 4.27=4.2 7 7 7 7 7... The number has infinitely many digits after the decimal symbol. Furthermore, these digits repeat themselves indefinitely. This means that the number is a repeating decimal number. Consequently, it can be written as the ratio of two integers. We can conclude that the first number is a rational number.

Rational Irrational
4.27

Classify 0.375

To categorize 0.375 we will consider whether we can express the number as the ratio of two integers. 0.375 = 375/1000 Since 375 and 1000 are both integers we can express 0.375 as a ratio of two integers, so this number is rational.

Rational Irrational
4.27
0.375

Classify 0.232342345...

We know that the dots at the end mean that the number continues indefinitely. 0.232342345... The number has infinitely many digits after the decimal point. Furthermore, these digits do not follow a specific pattern. This means that they neither terminate nor repeat. Consequently, the number cannot be written as a ratio of two integers. Therefore, we can conclude that the this number is an irrational number.

Rational Irrational
4.27 0.232342345...
0.375

Classify sqrt(62)

Here we will calculate the value of the given number by using a calculator.
sqrt(62)
7.874007...
This number also has infinitely many digits after the decimal point that do not follow a specific pattern. Because the number cannot be written as the ratio of two integers, the given decimal is an irrational number.
Rational Irrational
4.27 0.232342345...
0.375 sqrt(62)

Classify - 131

Next, we will think whether the last number is a rational number or an irrational number. - 13/1 ⇔ - 13/1 Since - 13 and 1 are both integers, we can express - 131 as a ratio of two integers, so this number is a rational number.

Rational Irrational
4.27 0.232342345...
0.375 sqrt(62)
- 13/1