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| 11 Theory slides |
| 10 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.
A ratio is a comparison of two quantities that describes how much of one thing there is compared to another. Ratios are commonly represented using colon notation or as fractions. They are read as the ratio of a to b,
where b is a non-zero number.
Fraction Form | Greatest Common Factor | Rewrite | Simplify | |
---|---|---|---|---|
Tearrik | 1527 | GCF(27,15)=3 | 5⋅39⋅3 | 59 |
Zain | 2545 | GCF(45,25)=5 | 5⋅59⋅5 | 59 |
Scaling is a way of creating equivalent ratios by multiplying or dividing the numerator and denominator of a ratio by the same number. Sometimes it is necessary to scale back and forward to find an equivalent ratio for a particular situation. Consider the following scenario.
Chocolate bars are on sale at 14 for $6. This ratio can be scaled up and down to find the cost of 21 chocolate bars.
614 | |
---|---|
Scaling Back | Scaling Forward |
6÷214÷2 | 3×37×3 |
37 | 921 |
Determine whether the given pair of ratios is equivalent.
Mark loves taking pictures with his camera. One of his favorite shots is of the Walter Pyramid. The picture has a height-to-width ratio of 3:4.
He wants to print it out and hang it on his bedroom wall, but he wants to print it in two different sizes equivalent to the original one.
Tables of equivalent ratios are called ratio tables. Consider the ratio table containing the distance Zain runs and the time it takes him to cover that distance.
Distance Run (Miles) | 1 | 2 | 3 | 4 |
---|---|---|---|---|
Time (Minutes) | 10 | 20 | 30 | 40 |
The ratios 101, 202, 303, and 404 are equivalent since each of them simplifies to a ratio of 101. A ratio table can be created by multiplying or dividing each quantity in a ratio by the same number, or by repeatedly adding or subtracting the ratio.
Mark received a new phone from his parents that has an excellent camera for his photography hobby.
The aspect ratio, which represents the relationship between height and width, of the main camera is 2:3. Mark created a ratio table to explore the equivalent ratios that his photos can have.
Height | 2 | A | 6 | 18 |
---|---|---|---|---|
Width | 3 | 6 | 9 | B |
However, the table is missing some values.
Height | 2 | A | 6 | 18 |
---|---|---|---|---|
Width | 3 | 6 | 9 | B |
Use the initial ratio of 2:3 to determine the ratio for the second column. Note that adding 3 to the width of the first ratio gives 6. This means that 2 can be added to the height of the first ratio to find the height that corresponds to a width of 6, which is the value of A.
Use the ratio of 6:9 to determine the corresponding width for a height of 18. Since 6⋅3=18, multiply 9 by 3 to get the value of B.
Therefore, A=4 and B=27.
Height, x | 2 | 4 | 6 | 18 |
---|---|---|---|---|
Width, y | 3 | 6 | 9 | 27 |
Because the table contains only positive values, only the first quadrant is required. Begin at the origin and move along the x-axis according to the number of units specified by the height. Then, move vertically the number of units specified by the width to graph each ratio.
This graph corresponds to option A.
Mark and Maya met up to compare the results of a five-day photo challenge. They each recorded the total number photos taken on each day in a table so that they could make a collage after finishing the challenge. The following table shows the data recorded by Maya and Mark.
Maya | Mark | ||
---|---|---|---|
Days | Photos | Days | Photos |
1 | 5 | 1 | 7 |
2 | 10 | 2 | 14 |
3 | 15 | 3 | 21 |
4 | 20 | 4 | 28 |
5 | 25 | 5 | 35 |
Maya | ||
---|---|---|
Days | Photos | (x,y) |
1 | 5 | (1,5) |
2 | 10 | (2,10) |
3 | 15 | (3,15) |
4 | 20 | (4,20) |
5 | 25 | (5,25) |
To graph the data, begin at the origin and move along the x-axis the number of units specified by the day. Then, move the number of units specified by the photos taken vertically to graph each ordered pair.
Before adding Mark's data to the graph, write each column of the table as an ordered pair.
Mark | ||
---|---|---|
Days | Photos | (x,y) |
1 | 7 | (1,7) |
2 | 14 | (2,14) |
3 | 21 | (3,21) |
4 | 28 | (4,28) |
5 | 35 | (5,35) |
Each ordered pair can now be added to the graph.
The graph corresponds to the one given in option B.
Maya | Mark | |
---|---|---|
Day, x | 1 | 1 |
Photos, y | 5 | 7 |
Maya's photo-to-day ratio is 5:1 and Mark's is 7:1. Now, look at the graph drawn in Part A.
Notice that both sets of points appear to fit in straight lines. However, the line for Mark is steeper than the line for Maya. The statements that are true about the ratios of photos taken to days passed have been identified.
Statement | True? |
---|---|
The ratio of photos to days for Maya is 5:1. | ✓ |
The ratio of photos to days for Mark is 7:1. | ✓ |
The line for Mark's data is steeper than the line for Maya's. | ✓ |
The ratio of days to photos for Maya is 5:1. | × |
The ratio of days to photos for Mark is 7:1. | × |
The line for Maya's data is steeper than the line for Mark's. | × |
Maya suggested Mark post his outstanding artwork on a website for people to buy. As a beginner seller, Mark received a graph that showed how much he would earn per photo sold.
Use the relationship between a pair of consecutive points on the graph to determine the ratio of money earned to photos sold. Apply that ratio to find the point for selling six photos on the graph.
Mark wants to know how much money he would earn for selling six photos. It is given that the ratio of money earned per photo sold remains constant. Consider the graph carefully. The points appear to fall in a straight line.
The point (4,6) is 2 units to the right and 3 units up from point (2,3).
This means that the ratio of the money earned to photos sold is 3:2 — Mark will earn $3 for every 2 photos sold. The amount of money he will earn by selling six photos can be determined using this ratio. Move 2 units to the right and 3 units up from (4,2) to locate this point.
Therefore, Mark would earn $9 for selling six photos.
This lesson covered some uses of equivalent ratios and how ratio tables can be used to find them. Equivalent ratios are particularly useful when scaling ratios to maintain proportions. Take a look at a ratio table that shows how many photos Maya's printer can print per minute.
Photos | 4 | 8 | 12 |
---|---|---|---|
Time (minutes) | 5 | 10 | 15 |
Now consider the ratio table that shows the same information for Mark's printer.
Photos | 20 | 24 | 28 |
---|---|---|---|
Time (minutes) | 25 | 30 | 35 |
Use the provided description to scale each given ratio and find a ratio equivalent to the original one.
Start by writing the given ratio in fraction form. 5:9 ⇔ 5/9 We multiply both the numerator and the denominator of a ratio by the same number to get an equivalent ratio. In this case, we need to scale the given ratio forward by 5 to find a ratio equivalent to 5:9. Let's use the fraction form of the ratio to find the equivalent ratio. 5* 5/9* 5=25/45 Therefore, scaling the given ratio 5:9 forward by 5 results in the equivalent ratio 25:45.
We will follow a similar process as in Part A to scale the given ratio back. Let's write it in fraction form first.
77:49 ⇔ 77/49
Since we want to scale the given ratio back by 7, we must divide both the numerator and denominator by 7 instead of multiplying. Let's do it!
77÷ 7/49÷ 7=11/7
Scaling the given ratio 77:49 back by 7 results in the equivalent ratio 11:7.
Consider the following ratio table.
x | 2 | A | 4 |
---|---|---|---|
y | B | 6 | 8 |
We want to find the values of A and B in the ratio table.
x | 2 | A | 4 |
---|---|---|---|
y | B | 6 | 8 |
Let's use the last column of the table to write the ratio of y to x. 8:4 ⇔ 8/4 Next, we can determine the unit ratio by dividing both quantities in this ratio by 4. 8÷ 4/4÷ 4=2/1 Let's use this unit ratio to find the missing values in the table. Remember, all ratios in a ratio table are equivalent. 2/1 ⇔ B/2 The denominator of B2 is twice the denominator of 21. This means that the numerator B should be twice the numerator 2. B=2* 2 ⇔ B=4 We can follow a similar process to find the value of A. 2/1 ⇔ 6/A In this case, the numerator of 6A is three times greater than the numerator of 21, the denominator A should be three times greater than the denominator 2. A=1* 3 ⇔ A=3 We found that A=3 and B=4. Let's complete the given ratio table.
x | 2 | 3 | 4 |
---|---|---|---|
y | 4 | 6 | 8 |
Ramsha and Tadeo recorded their typing speeds in a ratio table. The table below shows the number of words they can type over time.
Ramsha | Tadeo | ||
---|---|---|---|
Time (minutes) | Words Typed | Time (minutes) | Words Typed |
1 | 25 | 1 | 40 |
2 | 50 | 2 | 80 |
3 | 75 | 3 | 120 |
4 | 100 | 4 | 160 |
5 | 125 | 5 | 200 |
6 | 150 | 6 | 240 |
Identify the graph that displays their typing speeds.
Let's plot the data on a coordinate plane to determine which graph accurately displays the information from the ratio tables. In this case, the x-axis will represent the time and the y-axis will represent the number of words typed. Let's consider Ramsha's table.
Ramsha | |
---|---|
Time (minutes) | Words Typed |
1 | 25 |
2 | 50 |
3 | 75 |
4 | 100 |
5 | 125 |
6 | 150 |
We will move along the x-axis away from the origin the number of units specified by the time. We will then move vertically the number of units specified by the number of words typed to plot each ordered pair.
Now let's consider Tadeo's table.
Tadeo | |
---|---|
Time (minutes) | Words Typed |
1 | 40 |
2 | 80 |
3 | 120 |
4 | 160 |
5 | 200 |
6 | 240 |
We will follow a similar process to graph Tadeo's information.
This graph corresponds to option D.
We can determine which statements about the data are true by comparing the unit ratios in the first row of the ratio table.
Ramsha | Tadeo | ||
---|---|---|---|
Time (minutes) | Words Typed | Time (minutes) | Words Typed |
1 | 25 | 1 | 40 |
Ramsha typed 25 words per minute, while Tadeo typed 40 words per minute. Ramsha& &Tadeo 25words:1min & &40words:1min We can also consider the graph we drew in Part A.
This graph shows that both data sets follow a straight line. However, Tadeo's line is steeper than Ramsha's. With these findings, we can identify which statements are true about their data.
Statement | True? |
---|---|
Ramsha's ratio of words typed to time is 25:1. | ✓ |
Tadeo's ratio of words typed to time is 40:1. | ✓ |
The line for Tadeo's data is steeper than the line for Ramsha's. | ✓ |
Ramsha's ratio of words typed to time is 40:1. | * |
Tadeo's ratio of words typed to time is 25:1. | * |
The line for Ramsha's data is steeper than the line for Tadeo's. | * |
Magdalena made a logo that is 2 inches wide by 1 inch tall. Let's write the ratio of the width to height for Magdalena's logo. 2in.:1in. ⇔ 2in./1in. The enlarged logo must have the exact same proportions as Magdalena's logo, but it has to be eight times bigger. We can multiply the numerator and the denominator of Magdalena's logo ratio by 8 to get an equivalent ratio for the enlarged logo. 2 in.* 8/1 in. * 8=16in./8in. This means the enlarged logo's dimensions should be 16 inches in width and 8 inches in height.
We will find the cost of a package of 12 cupcakes, given that a package of 6 cupcakes costs $5. We can use this information to write the ratio for the number of cupcakes to their cost. 6cupcakes/$5 Since the price per cupcake is the same for every package, we can use this ratio to find the cost of 12 cupcakes. Let's write an equivalent ratio with a numerator of 12 cupcakes. 6cupcakes/$5=12cupcakes/ We are missing the denominator of this new ratio. Recall that to find an equivalent ratio, we multiply both quantities in the original ratio by the same number. Since 6* 2=12, we can multiply both quantities in the first ratio by 2 to find this equivalent ratio. 6cupcakes* 2/$5* 2=12cupcakes/$10 This means that a package of 12 cupcakes costs $10.