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This lesson provides a deep dive into the world of decimals, specifically focusing on terminating and repeating decimals. It explains how these types of decimals can be understood through the use of long division and their relation to rational numbers. For example, if one is trying to convert a fraction to a decimal, understanding whether the decimal will terminate or repeat can be crucial. This knowledge is not just theoretical; it has practical applications in various fields such as finance for calculating interest rates, in engineering for precise measurements, and even in everyday scenarios like splitting a bill. The aim is to equip the reader with the tools needed to tackle real-world problems that involve decimals.
Show less Show more expand_more| Student Learning Objectives: |
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| | 12 Theory slides |
| | 10 Exercises - Grade E - A |
| | Each lesson is meant to take 1-2 classroom sessions |
ccc Fraction & Mixed Number & Decimal 14/5 & 2 45 & 2.8 Decimal numbers can be grouped by what digits come after the decimal point. For example, what happens when we write 13 or 17 as a decimal? Do any digits repeat? This lesson explores different types of decimal number types and how to write them as fractions.
A rational number can be written as a decimal number using long division. Rewrite the fractions in the table as decimals.
| Fraction | Decimal |
|---|---|
| 2/9 | |
| 1/3 | |
| 3/4 | |
| 4/11 | |
| 3/8 |
Consider the following questions as a guide to classify decimals.
A repeating decimal number, or recurring decimal number, is a number in decimal form in which some digits after the decimal point repeat infinitely. The digits repeat their values at regular intervals and the infinitely repeated part is not zero. When writing the decimal, a line is drawn over the repeating portion to indicate the repetition.
| Repeating Decimal Numbers | ||
|---|---|---|
| Number | Notation | Fraction |
| 0.666666... | 0.6 | 2/3 |
| 1.533333... | 1.53 | 23/15 |
| 5.373737... | 5.37 | 532/99 |
A terminating decimal number is a number in decimal form with a finite number of digits. Terminating numbers can be written as fractions, which means that they are rational numbers.
| Terminating Decimal Numbers | ||
|---|---|---|
| Number | Fraction | |
| 0.5 | 1/2 | |
| 1.53 | 153/100 | |
| 52.372 | 13 093/250 | |
Determine whether the given number is a repeating decimal, a terminating decimal, or neither.
Fractions can be written as decimal numbers using long division. However, when the denominator of a fraction has a factor other than 2 or 5, the quotient will be a repeating decimal number. Consider the following fraction. 7/15 It is possible to write this fraction as a decimal in two steps.
A survey asked students what kinds of movies they like. The table shows the results.
| Genre | Number of Students |
|---|---|
| Action | 6 |
| Animation | 12 |
| Comedy | 4 |
| Science Fiction | 5 |
What fraction of the students prefer animation?
What fraction of the students prefer comedy?
How many students answered the survey? Write a fraction using the number of students that prefer animation and the total number of the students surveyed. Convert the fraction into a decimal number.
Write a fraction using the number of students that prefer comedy and the total number of the students surveyed. Convert the fraction into a decimal number.
Let's start by finding the total number of students who participated in the survey.
| Genre | Number of Students |
|---|---|
| Action | 6 |
| Animation | 12 |
| Comedy | 4 |
| Science Fiction | 5 |
| Total | 27 |
We can see that 27 students responded to the survey. Of these students, 12 prefer animation. We can represent this as a fraction by writing the part, the 12 students who like animation, over the whole, the 27 students surveyed. 12/27 Since the given options are decimals, let's converted into a decimal number using long division. We will continue until the remainder is 0 or a pattern appears.
It appears that the remainder will always repeat — in other words, the digit 4 in the quotient will always repeat. This means that the division resulted in a repeating decimal number. 12/27 = 0.444... The same value can also be written by drawing a bar over the repeating digit. 12/27 = 0.4 The answer is A.
From the table, we can see that four students like the comedy genre. This means that 427 of the students surveyed prefer comedies. Let's use long division again to rewrite it as a decimal. We will continue the division until the remainder is 0 or a pattern appears.
It looks like the remainder matches the difference after our first subtraction. Since the subtraction pattern will restart, more than one digit repeats in the quotient. 4/27 & = 0. 148148... Put a bar above those three digits to indicate the repetition. This repeating decimal corresponds to option C. 4/27 & = 0.148
Terminating decimal numbers can be converted to fractions by dividing the number by 10^n, where n is the number of decimal places. Terminating Decimal & & Fraction 0.56 & & 56/100 However, it is impossible to count the number of decimal places for repeating decimals because they have an infinite number of digits after the decimal point. Repeating Decimal & & Fraction 0.083 & & ? Even though they have an infinite number of digits, these numbers can be expressed as fractions. Follow these five steps to do so.
.LHS /9.=.RHS /9.
Cancel out common factors
Simplify quotient
Start by eliminating the decimal in the numerator to simplify the fraction. This can be done by multiplying the numerator and denominator by 10^2 because the numerator has 2 decimal places.
Since the greatest common factor of 900 and 75 is 75, we will simplify the fraction by dividing both the numerator and denominator by 75.
We found that x is equal to 112. Remember that x is also equal to 0.083. x = 0.83 and x = 1/12 Therefore, by the Transitive Property of Equality, the fraction is equal to the given repeating decimal number. 0.083=1/12
A survey asked students what kinds of movies they like. The table shows the results.
| Genre | Number of Students |
|---|---|
| Action | 6 |
| Animation | 12 |
| Comedy | 4 |
| Science Fiction | 5 |
Vincenzo selected two genres at random. He used a calculator to divide the number of students who prefer the two genres by the total number of students surveyed.
His calculator showed the result as 0.629629....
Write the result as a fraction.
Which two movie genres did Vincenzo choose?
Let x represent the repeating decimal and write an equation. How many repeating digits are there in the decimal number? Multiply the equation by a power of 10.
What is the numerator of the fraction we found in Part A? Determine which of the two types gives us a sum equal to this numerator.
The number shown on the calculator is a repeating decimal number because some digits after the decimal point repeat themselves.
0. 629 629... ⇔ 0.629 There are five steps to write this repeating decimal number as a fraction.
Let x be a variable that represents the given repeating decimal number. Write an equation by setting x equal to 0.629. x = 0.629
The repeated sequence of digits in the decimal is 629. There are three repeating digits, so n= 3.
Since n=3, multiply each side of the equation by 10^3, or 1000.
Now we subtract the original equation from the equation we created in Step 3. cr & 1000x = 629.629 [0.2em] - & x = 0.629 Consider the expanded forms of the numbers when performing this subtraction. cr & 1000x = 629.629629 ... [0.2em] - & x = 0.629629 ... & 999x = 629.000000 ... Since we can ignore the zeros after the decimal place, we get that 999x is equal to 629.
Let's solve our equation for x.
.LHS /999.=.RHS /999.
Cancel out common factors
Simplify quotient
We can check whether this fraction can be simplified by finding the greatest common factor (GCF) of the numerator and denominator. 629 = 17 * 37 999 = 3^3 * 37 The GCF(629,999) is 37. Finally, simplify the fraction by dividing both numerator and denominator by 37.
As a result, x is equal to 1727, which is equal to the given repeating number. 0.629=17/27
In Part A, it was found that 0.629 is equivalent to 1727. Notice that the denominator is the same as the total number of students surveyed, so 1727 should be the fraction that Vincenzo entered into the calculator. The numerator of this fraction is the sum of the students who prefer the two specific genres.
Now let's take a look at the table and determine which of the two genres gives a sum equal to 17.
| Genre | Number of Students |
|---|---|
| Action | 6 |
| Animation | 12 |
| Comedy | 4 |
| Science Fiction | 5 |
The number of students who prefer animation and science fiction is 17, so Vincenzo selected the animation and science fiction genres.
Write the given fraction as a repeating decimal and vice versa.
Here are some examples.
Repeating Decimal & & How to Submit 0.409 & ⇒ & 0.4 09 [0.6em] 0.9 & ⇒ & 0. 9
Greek mathematician and physicist Archimedes made many contributions to mathematics. One of his contributions was a method he used to approximate the value of π. π = 3.141592 ... Although this number cannot be expressed exactly as a ratio of two integers, Archimedes claimed that π was between 3 17 and 3 1071. Was he correct?
First, rewrite 3 17 as an improper fraction.
Next, use long division to divide the numerator by the denominator of the fraction.
The mixed number is equal to 3.142857.... 3 17 & = 3.142857...
Let's follow the same steps as before to write 3 1071 as a decimal. We start by rewriting the mixed number as an improper fraction.
Next, divide the numerator 223 by the denominator 71. Calculate to 6 decimal places.
We found that 3 1071 is equal to 3.140845 .... 3 1071 = 3.140845...
Now we can compare the three numbers. 3 17 &= 3.142857... 3 1071 &= 3.140845... π &= 3.141592... Notice that the first three digits of the numbers are all the same. 3 17 &= 3.142857... 3 1071 &= 3.140845... π &= 3.141592... This means that the digits in the thousandths place must be compared. 3 17 &= 3.14 2857... 3 1071 &= 3.14 0845... π &= 3.14 1592... The number with the greatest digit in the thousandth place is the greatest, and the number with the least digit is the least. 3.140845... < 3.141592... < 3.142857... ⇓ 3 1071 < π < 3 17 Therefore, π is between 3 1071 and 3 17. Archimedes was correct. The answer is B.
The circumference of the circle would be somewhere between the perimeters of the polygons. Archimedes calculated the perimeters of the polygons using geometric arguments.
His final estimate for π use a shape with 96 sides. His calculations gave a range between 3 1071 and 3 17. 3 1071 < π < 3 17 Of course, he found this result with pen and paper, without the help of a computer or calculator. Amazing!
This lesson presented two types of decimal numbers, terminating and repeating decimals, and methods for converting both to and from fractions. Now comes a tough question! What about decimal numbers that have an infinite number of places but do not repeat? These decimals are called irrational numbers. Take, for example, π. π = 3.141592 ... We do not see any repeating patterns in this decimal number, so it has no end. The number is irrational. Here are a few other commonly used irrational numbers.
| Some Irrational Numbers | |
|---|---|
| Euler's number, e | 2.718281 ... |
| Golden ratio, ϕ | 1.618033 ... |
| sqrt(2) | 1.414213 ... |
Irrational numbers cannot be converted into rational numbers. This diagram shows how decimal numbers are classified.
We want to determine whether the given number is a repeating decimal. Let's begin by recalling the definitions.
| Definition | |
|---|---|
| Terminating Decimal | A decimal number whose digits after the decimal point are finite. When written as a fraction and dividing the numerator by the denominator, the remainder is 0. |
| Repeating Decimal | A decimal number whose some digits after the decimal point repeat infinitely. When written as a fraction and dividing the numerator by the denominator, the remainder will never be 0 because the products and differences repeat. |
With this in mind, let's take a look at the given number. 0.1415 Notice that a bar is drawn over two digits after the decimal point. This means that the digits 1 and 5 repeat infinitely. Because of this, we can say that 0.1415 is a repeating decimal.
We know that the dots at the end of a decimal number mean that the number continues indefinitely.
0.141516 ...
This number has infinitely many digits after the decimal point. Additionally, the digits do not appear to repeat. Therefore, the decimal number is neither terminating nor repeating. Additionally, the number cannot be written as the ratio of two integers, which means that it is an irrational number.
Let's take a look at our last number.
0.141
Notice that there are only three digits after the decimal point, 141, with no dots to indicate that the decimal continues. This means the number of digits is finite. Because of this, we can say that 0.141 is a terminating decimal.
We want to write the given fraction as a decimal. 9/11 We will divide the numerator by the denominator. Let's do it by using long division!
We can stop dividing because we get the same remainders as we continue — the remainder will never become 0. Because of this, we can conclude that the quotient is a repeating decimal. 9/11 = 0.818181... We see that the number has two repeating digits, 8 and 1, so we can also write the decimal with a bar above those digits. 9/11 = 0.81
We are given a mixed number.
1 916
Before we convert this number into a decimal, let's rewrite it as an improper fraction. This will make it easier for us to convert it into decimal form.
The mixed number 1 916 is equal to 2516. Next we will divide the numerator by the denominator to write this number in decimal form.
We eventually got 0 as the remainder, so we can say that 1 916 written in decimal form is a terminating decimal and is equal to 1.5625. 1 916 = 1.5625
We want to write the given repeating decimal number as a fraction. 0.356 We will follow five steps to rewrite it as a fraction.
Let's do it!
Let's use the variable x to represent the given repeating decimal number. We can write an equation by setting this variable equal to 0.356. x = 0.356
For the given decimal, the digit that repeats is 6. The number has one repeating digit, so n= 1.
Now we multiply each side of the equation by 10^1, or 10, since we found that n=1.
Now we will subtract the original equation from the equation we found in Step 3. cr & 10x = 3.566 - & x = 0.356 Let's expand the decimals a bit to make it easier to see how the repeating digits cancel each other out. cr & 10x = 3.566666 ... - & x = 0.356666 ... & 9x = 3.210000 ... We can ignore the zeros because they do not change the value of the difference. We found that 9x = 3.21.
Lastly, we solve the final equation for x. We need to divide both sides of the equation by 9 to isolate x on the left-hand side.
We can eliminate the decimal in the numerator by multiplying both the numerator and the denominator by 100. This will move the decimal point in the numerator two place to the right and make it a whole number.
Finally, we will check if this fraction can be simplified. Let's find the greatest common factor (GCF) of the numerator and denominator. 321 = 3 * 107 900 = 3^2 * 10^2 The GCF of the numbers is 3. Let's simplify the fraction by dividing both the numerator and the denominator by 3.
We found that x is equal to 107300. We can conclude that the given repeating number is equal to 107300. 0.356=107/300
We are given a negative repeating decimal.
- 4.023
Let's ignore the negative sign and write the number as a fraction. We will put the negative sign back at the end.
4.023
We will follow the same steps we followed in Part A to write this number as a fraction.
Let's use x to represent our decimal. x = 4.023 We can see that the number has two repeating digits, meaning that n= 2.
Now we multiply each side of the equation by 10 to the power of 2, or 100, because n=2.
Now we will subtract the original equation from the equation we found in Step 3. cr & 100x = 402.323 - & x = 4.023 Let's use the expanded forms of the numbers to make it easier to see how the repeating digits cancel each other out. cr & 100x = 402.3232323 ... - & x = 4.0232323 ... & 99x = 398.3000000 ... Since we can ignore the zeros, we have 99x = 398.3.
Finally, we solve the new equation for x. Dividing both sides of the equation by 99 will isolate x on the left-hand side.
We can eliminate the decimal in the numerator by multiplying both the numerator and the denominator by 10.
Let's check if the numerator and denominator have any common factors. 3983 & = 7 * 569 990 & = 2 * 3^2 * 5 11 The numbers do not have any common factors, so we cannot simplify the fraction. We can conclude that the given repeating number is 3983990. 4.023=3983/990 We can also write this improper fraction as a mixed number.
We found that 4.023=4 23990. Therefore, - 4.023 is equal to - 4 23990. - 4.023 = - 4 23/990
Ignacio draws the diagram below to represent a fraction.
Which of the following decimal numbers is equal to the fraction modeled by Ignacio's diagram?
There are 9 equal parts in the diagram, 5 of which are shaded.
We can then say that this model represents the fraction 59. We want to write this fraction as a decimal number. We can divide the numerator by the denominator to find its decimal form. Let's use long division to do it!
We can see that a specific pattern starts to repeat itself after a few steps. This means that the decimal is a repeating decimal. 5/9 = 0.5555... We can write the decimal using bar notation. Remember, the bar goes over the decimal part that repeats itself! 5/9 = 0.5 This corresponds option B.
Ramsha arranges the following rational numbers from least to greatest along a number line. 7/3, - 9/10, 1 1318, - 2, - 3.1 Which number line did Ramsha draw?
We will write all the given numbers as decimals so we can easily compare them. 7/3, - 9/10, 1 1318, - 2, - 3.1 We see that - 3.1 is a repeating decimal and - 2 is an integer, so they are already in decimal form. Let's rewrite the other numbers.
Let's start with the improper fraction 73. We will use long division to divide 7 by 3.
We keep getting the same remainder as we continue dividing. Therefore, this is a repeating decimal. 7/3 = 2.3
The next number is - 910. Since the denominator is a multiple of 10, this is a terminating decimal. - 9/10 =- 0.9
The third number is a mixed number. Let's first write it as an improper fraction.
Now we use long division again to write 3118 as a decimal number.
We eventually start getting the same remainder 4 at each step. Let's stop here because the quotient is a repeating decimal. The mixed number 1 1313 is equivalent to 1.72. 1 1318 = 1.72
We have now found the decimal forms of all of the numbers!
| Numbers | Decimal Form |
|---|---|
| 7/3 | 2.3 |
| - 9/10 | - 0.9 |
| 1 1318 | 1.72 |
| - 2 | - 2 |
| - 3.1 | - 3.1 |
As we can see, - 3.1 is the least and 2.3 is the greatest. - 3.1 < - 2 < - 0.9 < 1.72 < 2.3 We can show these number on a number line.
This number line corresponds to option C.