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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.
However, the graph does not provide information on Mark's earnings if he sells six photos. Assuming the ratio of photos sold to earnings remains constant, how much money would Mark earn from selling six photos?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 |