Mathematics
Grade 8
15 min
Division with decimal quotients
Division with decimal quotients
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1
Introduction & Learning Objectives
Learning Objectives
Calculate the scale factor between two similar figures when the ratio results in a decimal.
Determine if two figures are similar by dividing corresponding side lengths to find a consistent decimal ratio.
Use long division to find a decimal quotient to a specified number of decimal places.
Solve for an unknown side length in a similar figure, resulting in a decimal answer.
Interpret a decimal quotient as a scale factor of enlargement (k > 1) or reduction (0 < k < 1).
Accurately place the decimal point in the quotient when dividing integers.
Apply division with decimal quotients to solve real-world problems involving scale models and maps.
Ever tried to resize a picture and it ended up stretched and weird? 🖼️ To keep the shape perfect, every part...
2
Key Concepts & Vocabulary
TermDefinitionExample
Decimal QuotientThe result of a division problem that includes a decimal point. This occurs when the divisor does not divide the dividend into a whole number.10 ÷ 4 = 2.5. The decimal quotient is 2.5.
SimilarityTwo geometric figures are similar if they have the exact same shape but can be different sizes. Their corresponding angles are equal, and the ratio of their corresponding side lengths is constant.A 3-4-5 right triangle is similar to a 6-8-10 right triangle because all sides of the second triangle are twice the length of the sides of the first.
Corresponding SidesSides that are in the same relative position in two similar figures.In two similar rectangles ABCD and WXYZ, side AB corresponds to side WX.
Scale Factor (k)The constant ratio used to enlarge or reduce...
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Core Formulas
Scale Factor Formula
k = \frac{\text{Image Side Length}}{\text{Pre-image Side Length}}
To find the scale factor (k) that transforms a pre-image into an image, divide the length of a side on the image by the length of the corresponding side on the pre-image. The result is often a decimal.
Decimal Placement in Long Division
Dividend ÷ Divisor = Quotient
To perform division that results in a decimal, place a decimal point after the last digit of the dividend and add trailing zeros. The decimal point in the quotient goes directly above the decimal point in the dividend.
Proportionality in Similar Figures
\frac{A'B'}{AB} = \frac{B'C'}{BC} = \frac{C'A'}{CA} = k
For two similar triangles ABC and A'B'C', the ratio of any pair of c...
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Challenging
Rectangle X has a length of 20 cm and a width of 12 cm. It is reduced to create a similar Rectangle Y, which has a length of 15 cm. What is the area of Rectangle Y?
A.135 cm²
B.240 cm²
C.180 cm²
D.9 cm²
Challenging
A figure was enlarged by a scale factor of 2.5 to create an image. If one side of the image measures 18 cm, what was the length of the corresponding side on the original pre-image?
A.45 cm
B.7.2 cm
C.7.5 cm
D.20.5 cm
Challenging
A student is calculating the scale factor from a pre-image side of 16 cm to an image side of 2 cm. Their work shows the quotient as 1.25. What is their primary error?
A.The subtraction in their long division was incorrect.
B.The student divided pre-image by image instead of image by pre-image.
C.The decimal point in the quotient is misplaced; it should be 0.125.
D.The student stopped the division too soon.
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