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| 12 Theory slides |
| 9 Exercises - Grade E - A |
| Each lesson is meant to take 1-2 classroom sessions |
Here are a few recommended readings before getting started with this lesson.
Background to Help Understand Numbers
Background to Help Understand Multiples
Imagine that two numbers need to be compared. Consider this pair of numbers. 15 % and 0.32 Which one is greater? Which is less? The first thing to check is whether the numbers have the same form. In this case, the first number is a percent, while the second is a decimal number. ccc Percent & & Decimal ↓ & & ↓ 15 % & & 0.32 They do not have the same form, so they cannot be directly compared. It is like comparing strawberries and dogs — they are just not comparable because they belong to totally different categories and have drastically different features.
It is the same way with numbers. Numbers can only be compared if they are written in the same format. cccc Percents: & 15 % & vs. & 54 % Decimals: & 0.32 & vs. & 2.19 Therefore, to compare two numbers, always begin by making sure that they have the same form. If they do, go ahead and compare them! If they do not, first convert one or both numbers such that they are written in the same format.
Tiffaniqua:& 254.6 LaShay:& 279.5 Kevin:& 252 All these speeds are given as decimal numbers. One way to order these numbers from least to greatest is to compare them digit by digit. Another method is to plot them as points on a number line. On a number line, the farther to the right the number is, the greater it is.
Notice that point K, which represents Kevin's speed, is the least because it is farthest to the left. Next comes the point T, Tiffaniqua's speed. Finally, point L is the farthest to the right, meaning that LaShay's speed is the greatest. ccccc K & & T && L ↓ & &↓ && ↓ 252&<& 254.6&<&279.5 Therefore, Kevin is the slowest typist at the moment, Tiffaniqua is in the middle, and LaShay is the fastest. Not to worry — Kevin still has time to practice and beat Tiffaniqua and LaShay.
125 %, 1.03, 98 %, 1.17 To be able to compare the numbers, they should be written in the same form — either all as percents or all as decimal numbers. Rewrite the decimals as percents by multiplying them by 100 and adding the percent sign. 1.03* 100=103 % 1.17* 100=117 % Now all the numbers are written as percents! 125 %, 103 %, 98 %, 117 % Compare the numbers by plotting them on a number line.
Finally, the percents can be ordered from least to greatest. cccc 98 %, & 103 %, &117 %, &125 % [0.1cm] ↓ & ↓ & ↓ & ↓ [0.1cm] 98 %, & 1.03, & 1.17, & 125 %
Consider a pair of fractions. How can the fractions be compared when they have different numerators and denominators? 4/7 and 5/8 Both fractions represent a part of a whole, but it is difficult to say which one is greater straight away. The best way to compare these fractions would be to convert them to equivalent fractions that have the same denominator. 4/7 → ?/New Denom. and ?/New Denom. ← 5/8 When two fractions have the same denominator, they are said to have a common denominator.
A common denominator is a denominator that is shared between two or more fractions. Consider a few examples.
Pair of Fractions | Common Denominator |
---|---|
2/3 and 5/3 | 3 |
8/10 and 5/10 | 10 |
11/17 and 6/17 | 17 |
Fractions can always be rewritten to all have a common denominator. This process requires writing equivalent fractions by expanding or simplifying the fractions. As an example, take a look at a pair of fractions with different denominators. 1/3 and 1/2 These fractions are in their simplest form, which means that they can only be expanded. Write the multiples of their denominators, 3 and 2, to find the factor of expansion. Multiples of3:& 3, 6, 9, 12, 15, 18, ... Multiples of2:& 2, 4, 6, 8, 10, 12, 14, ... There are two potential common denominators in these lists. Expand the first fraction by 123= 4 and the second fraction by 122= 6 to make them have a common denominator of 12. 1 * 4/3 * 4&=4/12 [0.3cm] 1 * 6/2 * 6&=6/12 Now the fractions share a common denominator.
4/12 and 6/12There are a lot of possible common denominators that fractions can have. However, it is almost always easier to deal with smaller numbers. This is when the least common denominator comes in handy!
The least common denominator (LCD) of two fractions is the least common multiple (LCM) of the denominators of the fractions. In other words, the least common denominator is the smallest of all the common denominators. Some examples are provided in the table below.
Fractions | Denominators | Multiples of Denominators | Common Denominators | LCM of Denominators (LCD) |
---|---|---|---|---|
2/3 and 1/2 | 3 and 2 | Multiples of3:& 3, 6, 9, 12, 15, ... Multiples of2:& 2, 4, 6, 8, 10, 12, ... | 6, 12 | 6 |
5/6 and 1/4 | 6 and 4 | Multiples of6:& 6, 12, 18, 24, 30, ... Multiples of4:& 4, 8, 12, 16, 20, 24, ... | 12, 24 | 12 |
1/4 and 5/2 | 4 and 2 | Multiples of4:& 4, 8, 12, ... Multiples of2:& 2, 4, 6, 8, 10, 12, ... | 4, 8, 12 | 4 |
The least common denominator is used when adding or subtracting fractions with different denominators.
2/10 - 1/11 = 22/110_(LCD) - 10/110_(LCD)To sum up, finding the least common denominator is the same as finding the least common multiple of the denominators. When fractions have a common denominator, which is most often the LCD, they are ready to be compared by comparing their numerators.
Fractions | 4/11 and 9/11 |
---|---|
Numerators | 4<9 |
Conclusion | 4/11<9/11 |
There are cases when two fractions share the same numerator. In this case, the fractions can be compared based on their denominators. Consider a pair of fractions. 5/7 and 5/16 When fractions have the same denominator, the fraction with the greater numerator is greater. However, when fractions have the same numerator, it is the opposite — the fraction with the smaller denominator is greater.
Same Denominator | Same Numerator |
---|---|
The greater numerator, the greater the fraction. | The smaller denominator, the greater the fraction. |
Since 7 is less than 16, the first fraction must be greater. 5/7> 5/16 To understand why this is true, think of a whole represented by 1. The denominators indicate how many pieces this whole is split into. Here, it is split into 7 pieces for the first fraction and 16 pieces for the second fraction.
Notice that the 7 pieces of the first fraction are much larger than the 16 pieces of the second. The numerator of each fraction indicates how many pieces get picked. Since the numerators are the same, 5 pieces are selected from each whole. Which fraction has a larger selected section?
The total selected area is greater in the first fraction than in the second because each of the pieces is bigger. This is why the fraction with the smaller denominator is greater if the numerators are the same.
Consider the given pair of fractions. Which one is greater? Choose the correct sign to complete the expression. If necessary, rewrite the fractions such that they have a common denominator.
Rewrite the fractions so that they have a common denominator. Find it by determining the LCM of the denominators.
Four fractions need to be ordered from greatest to least. 5/6, 5/20, 2/3, 1/5 They have different numerators and denominators. Rewrite them such that they have a common denominator to be able to compare them. Start by finding the LCM of the denominators of the fractions to find a candidate for a common denominator. Denominators 6, 20, 3, 5 First, list the multiples of all the numbers and try to find the least common one. Multiples of6:& 6, 12, 18, ..., 54, 60, ... Multiples of20:& 20, 40, 60, 80, 100 ... Multiples of3:& 3, 6, 9, 12, ..., 57, 60 ... Multiples of5:& 5, 10, 15, 20, ..., 55, 60 ... The LCM of the numbers is 60. Next, divide 60 by each of the numbers to find by which factor each fraction should be expanded.
Denominator | Calculating the Quotient | Factor |
---|---|---|
6 | 60/6 | 10 |
20 | 60/20 | 3 |
3 | 60/3 | 20 |
5 | 60/5 | 12 |
Fraction | Equivalent Fraction |
---|---|
5/6 | 50/60 |
5/20 | 15/60 |
2/3 | 40/60 |
1/5 | 12/60 |
Finally, the fractions with the same denominator can be compared by looking at their numerators and ordering them from greatest to least. ccccccc 50/60&>& 40/60&>&15/60&>&12/60 [0.3cm] ↓ & &↓ & & ↓ & & ↓ [0.3cm] 5/6 & &2/3 & &5/20 & &1/5
Tiffaniqua, LaShay, Kevin, and one of their classmates are working on a biology project comparing four different flowers. Each of them was assigned a specific flower. After some research time, they met up to discuss what they found out.
Rewrite the numbers so that they are in the same form. Then, plot the numbers on a number line to help place them in order.
Consider the numbers found by the students during their research about different flowers. One number is a fraction, one is a decimal number, one is a mixed number, and one is a percent. 4/5, 0.91, 1 29, 78 % To compare the numbers, they need to be written in the same form. It does not matter which format is chosen, but all numbers will be rewritten as percents in this solution.
Gather all the numbers and their corresponding percent forms. cccc 4/5 & 0.91 & 1 29 & 78 % ↓ & ↓ & ↓ & ↓ [0.2cm] 80 % & 91 % & 122 % & 78 % To compare the percents, ignore the percent signs and plot the numbers on a number line.
The given numbers can finally be ordered from least to greatest. ccccccc 78 % & & 80 % & & 91 % & & 122 % [0.2cm] ↓ & & ↓ & & ↓ & & ↓ [0.2cm] 78 % & < & 4/5 & < & 0.91 & < &1 29
Let's start by analyzing the given list of numbers. 41 %, 0.17, 29 %, 0.35 There are two percents and two decimal numbers. Let's rewrite them so that all of the numbers are in the same form so that we can easily compare them. Percents:& 41 %, 29 % Decimals:& 0.17, 0.35 Let's rewrite the decimals as percents. For this, multiply the decimals by 100 and add a percent sign. We will start with 0.17. Move the decimal point two places to the right to multiply it by 100.
As we can see, 0.17 is equivalent to 17 %. 0.17* 100=17 % We can rewrite 0.35 into a percent in a similar manner. Let's move the decimal point two places to the right and add a percent sign.
We can see that 0.35 is equal to 35 %. 0.35* 100=35 % All the numbers are written in percent form now. cccc 41 % & 0.17 & 29 % & 0.35 [0.2cm] ↓ & ↓ & ↓ & ↓ [0.2cm] 41 % & 17 % & 29 % & 35 % Let's plot these numbers on a number line to help us order them from least to greatest. Remember that the farther to the right a number is located on the line, the greater it is.
Finally, the numbers can finally be ordered from the least to the greatest. ccccccc 17 % &< & 29 % &< & 35 % &< & 41 % [0.2cm] ↓ & & ↓ & & ↓ & & ↓ [0.2cm] 0.17, & & 29 %, & & 0.35, & & 41 %
We are given two fractions and two percents. 2/5, 46 %, 3/8, 38 % In order to compare these numbers, we need to rewrite them to be in the same form. Let's rewrite the fractions into percents. We will start with 25. First, divide the numerator by the denominator by using long division.
Next, multiply the decimal number by 100 and add a percent sign. 0.4* 100=40 % We can rewrite 38 as a percent in a similar fashion. Let's divide 3 by 8.
Now, multiply the decimal number by 100 and add a percent sign. 0.375* 100=37.5 % As we can see, 38 is equivalent to 37.5 %. All the numbers are now written in percent form! cccc 2/5, & 46 %, & 3/8, & 38 % [0.2cm] ↓ & ↓ & ↓ & ↓ [0.2cm] 40 %, & 46 %, & 37.5 %, & 38 % Finally, we can order the number from least to greatest by comparing their percent form. cccc 37.5 % &< & 38 % &< & 40 % &< & 46 % [0.2cm] ↑ & & ↑ & & ↑ & & ↑ [0.2cm] 3/8, & & 38 %, & & 2/5, & & 46 %
Tearrik needs to compare the speeds of different vehicles and animals. He wrote their speeds as they compare to 100 kilometers per hour, which he set as 100 %.
We are given four different numbers. 48 %, 227 %, 0.65, 3.1 Two of these numbers are percents and two are decimal numbers. We need to rewrite them so that they are in the same form in order to be able to compare them. Percents:& 48 %, 227 % Decimals:& 0.65, 3.1 Let's rewrite the numbers as decimals. To do this, divide the percents by 100 and remove the percent signs. We will start with 48 %. Move the decimal point two places to the left to divide it by 100.
As we can see, 48 % is equivalent to 0.48. 48 %÷ 100=0.48 We can rewrite 227 % as a percent in a similar manner. Let's move the decimal point two places to the left.
We can see that 227 % is the same as 2.27. 227 %÷ 100=2.27 All the numbers are now written in decimal form! cccc 48 % & 227 % & 0.65 & 3.1 [0.2cm] ↓ & ↓ & ↓ & ↓ [0.2cm] 0.48 & 2.27 & 0.65 & 3.1 Finally, let's compare these numbers and order them from greatest to least. ccccccc 3.1 &> & 2.27 &> & 0.65 &> & 0.48 [0.2cm] ↓ & & ↓ & & ↓ & & ↓ [0.2cm] 3.1, & & 227 %, & & 0.65, & & 48 % [0.2cm] ↓ & & ↓ & & ↓ & & ↓ [0.2cm] Racing car & & Railway car & & Tiger & & Horse Therefore, the racing car is the fastest, followed by the railway car, the tiger, and, finally, the horse.
Tearrik and Ali are solving their math homework. They need to compare a percent and a mixed number.
The boys need to compare two numbers, a mixed number and a percent. 4 59 and 462 % Let's analyze each solution step by step.
Tearrik decides to rewrite the mixed number as a percent to be able to compare the numbers. First, he converts the mixed number into an improper fraction by applying the corresponding formula. a bc=a* c+b/c Let's check if he applied the formula correctly.
The improper fraction that corresponds to 4 59 is 419. Tearrik calculated this step correctly. Next, he divides the numerator by the denominator using long division.
The quotient is about 4.55. Next, Tearrik needs to multiply this decimal number by 100 and add a percent sign.
4.55* 100=455 %
This means that the mixed number is equivalent to about 455 %. Finally, Tearrik compares the percents and concludes that 462 % is greater than 455 %.
455 % < 462 %
Tearrik's solution is absolutely correct!
Let's now consider Ali's solution. His first step is the same as Tearrik's. He rewrites the mixed number as an improper fraction. 4 59=41/9 ✓ Next, Ali rewrites the fraction as a percent. For this, he divides the numerator by the denominator. 41/9=4.55 He rounds the number to one decimal place and writes 4.6 %. However, he does not realize that he only found the corresponding decimal, and not the percent. To find the percent, he would also need to multiply the result by 100. This means that this step is incorrect. 41/9≈ 4.6 % * Therefore, Ali's solution is incorrect. Only Tearrik is correct.