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| 12 Theory slides |
| 10 Exercises - Grade E - A |
| Each lesson is meant to take 1-2 classroom sessions |
Fraction & Mixed Number & Decimal 14/5 & 2 45 & 2.8 Decimal numbers can be classified based on the digits after the decimal point. As an example, consider the decimal number corresponding to 13. Is there a repeating digit? How about the decimal equivalent of 17? This lesson explores decimal number types and develops methods for converting them into fractions.
Here are a few recommended readings before getting started with this lesson.
A rational number can be represented as a decimal number with the help of the long division method. Rewrite the fractions shown 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 express such a number.
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.
The fraction was found to be a repeating decimal number. 7/15 = 0.4666... The digit that repeats is 6, so a bar is drawn over that digit. 7/15 = 0.46
Vincenzo conducts a survey to find out what kind of movies his classmates like. The table shows the information he gathered from the survey.
Genre | Number of Students |
---|---|
Action | 6 |
Animation | 12 |
Comedy | 4 |
Science Fiction | 5 |
Genre | Number of Students |
---|---|
Action | 6 |
Animation | 12 |
Comedy | 4 |
Science Fiction | 5 |
Total | 27 |
For the given decimal, the repeating digit is 3. x = 0.083 There is only one digit with a bar above it. This means n= 1.
Now subtract the original equation from the equation obtained in Step 3. cl & 10x = 0.83 - & x = 0.083 Writing the decimals without using bar notation can make subtraction easier to understand. cl & 10x = 0.83333 ... - & x = 0.08333 ... & 9x = 0.75000 ... The zeros can be ignored. It is found that 9x is equal to 0.75.
.LHS /9.=.RHS /9.
Cancel out common factors
Simplify quotient
Vincenzo is organizing the information he gathered from his survey.
Genre | Number of Students |
---|---|
Action | 6 |
Animation | 12 |
Comedy | 4 |
Science Fiction | 5 |
He 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.
His calculator showed the result as 0.629629629....
0. 629 629 629... ⇔ 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.
Now subtract the original equation from the equation obtained in Step 3. cr & 1000x = 629.629 [0.6em] - & x = 0.629 Consider the expanded forms of the numbers when performing this subtraction. cr & 1000x = 629.629629 ... - & x = 0.629629 ... & 999x = 629.000000 ... Since the zeros can be ignored, 999x is equal to 629.
.LHS /999.=.RHS /999.
Cancel out common factors
Simplify quotient
Now 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. Therefore, Vincenzo selected the animation and science fiction genres.
If the answer is a repeating decimal, do the following to submit the answer.
Here are some examples. Repeating Decimal & & How to Submit 0.409 & ⇒ & 0.4 09 [0.6em] 0.9 & ⇒ & 0. 9
Write the mixed numbers as decimals.
Archimedes believed that π was between two rational numbers, 3 17 and 3 1071. π = 3.141592... To check whether Archimedes was correct, both of the numbers will be written as a decimal. Since the first six decimal places of π are given, the numbers will be calculated up to 6 decimal places. In this way, the numbers can be compared.
Now that the decimal forms of both numbers have been found, the numbers can be compared. 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 thousandth 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.
This lesson presented two types of decimal numbers, terminating and repeating decimals. The lesson also introduced methods for converting both fractions. Now comes a tough question! Are there decimal numbers that have an infinite number of places but do not repeat? The answer is yes and they are called irrational numbers. Take, for example, π. π = 3.141592653 ... No repeating patterns are seen in this type of decimal number, so their decimal representations have no end. 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. All that can be done is to get better and better approximations. The diagram shows how decimal numbers are classified.
Zosia knows that three one-thirds is equal to one. 1/3 + 1/3 + 1/3 = 1 She then remembers that 13 can also be written as a repeating decimal. She adds these numbers as decimals again and gets 0.999999.... cr & 0.333333 ... & 0.333333 ... +& 0.333333 ... & 0.999999 ... Consider the following question to determine whether Zosia's calculations are correct.
Let's write the given repeating decimal as a fraction. 0.999999 ... We will follow five steps to rewrite it.
Let's do it!
Let x represent the given repeating decimal number. x = 0.999999 ... Notice that there is only one repeating digit, 9. This means that n= 1.
We will multiply both sides of the equation by 10^1, or 10, because n= 1.
Now we will subtract the original equation from the equation written in Step 3. cr & 10x = 9.999999 ... - & x = 0.999999 ... & 9x = 9.000000 ... We found that 9x = 9.
Finally, we will divide both sides of the equation by 9 to find the value of x.
We found that x is equal to 99, or simply 1. We can conclude that 0.999999 ... is equal to 1. 0.999999 ... = 1
Alternatively, we can use the decimal expansion of 19, which is equal to 0.111111.... 1/9 = 0.111111... When we multiply both sides by 9, we get the following. 9 * 1/9 = 0.999999... On the left hand side, we get 99, or 1.
In Part A, we found that 0.999999 ... is equal to 1. 0.999999 ... = 1 At first glance, it would be easy for us to say that the left-hand side will never equal the right. This is because we cannot easily get a sense of infinitely many 9s. However, the equation is actually true because of the infinite number of 9s on the left. We showed how this is possible with our calculations in Part A. cr & 0.333333 ... & 0.333333 ... +& 0.333333 ... & 0.999999 ... cr & 0.333333 ... & 0.333333 ... +& 0.333333 ... & 1.000000 ... Therefore, all of Zosia's calculations are correct. Three one-thirds, or 33, can be written as 0.999999... or as 1.000000 ....