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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
A common denominator is a denominator that is shared between two or more fractions. Consider a few examples.
Pair of Fractions | Common Denominator |
---|---|
32 and 35 | 3 |
108 and 105 | 10 |
1711 and 176 | 17 |
There 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) |
---|---|---|---|---|
32 and 21 | 3 and 2 | Multiples of 3:Multiples of 2: 3,6,9,12,15,… 2,4,6,8,10,12,…
|
6, 12 | 6 |
65 and 41 | 6 and 4 | Multiples of 6:Multiples of 4: 6,12,18,24,30,… 4,8,12,16,20,24,…
|
12, 24 | 12 |
41 and 25 | 4 and 2 | Multiples of 4:Multiples of 2: 4,8,12,… 2,4,6,8,10,12,…
|
4, 8, 12 | 4 |
The least common denominator is used when adding or subtracting fractions with different denominators.
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 | 114 and 119 |
---|---|
Numerators | 4<9 |
Conclusion | 114<119 |
Same Denominator | Same Numerator |
---|---|
The greater numerator, the greater the fraction. | The smaller denominator, the greater the 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.
Denominator | Calculating the Quotient | Factor |
---|---|---|
6 | 660 | 10 |
20 | 2060 | 3 |
3 | 360 | 20 |
5 | 560 | 12 |
Fraction | Equivalent Fraction |
---|---|
65 | 6050 |
205 | 6015 |
32 | 6040 |
51 | 6012 |
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.
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.