### Topics

- 增殖
- Decimals
- Area Model
- Factors
- Partial Products

- 增殖
- Decimals
- Area Model
- Factors
- Partial Products

- Recognize that area represents the product of two numbers and is additive.
- Develop and justify a strategy that uses the area model to simplify a decimal multiplication problem.
- Devise a strategy to determine the product of two rational numbers (or an integer and a rational number) by representing the product as an area or the sum of areas.
- Use an area model to understand why multiplying a given number by a decimal less than 1 results in a product smaller than the given number.
- Interpret the product of two rational numbers using base-ten tiles

5.NF.B.5b

Explaining why multiplying a given number by a fraction greater than 1 results in a product greater than the given number (recognizing multiplication by whole numbers greater than 1 as a familiar case); explaining why multiplying a given number by a fraction less than 1 results in a product smaller than the given number; and relating the principle of fraction equivalence*a*/*b*= (*n*×*a*)/(*n*×*b*) to the effect of multiplying*a*/*b*by 1.5.NF.B.5a

Comparing the size of a product to the size of one factor on the basis of the size of the other factor, without performing the indicated multiplication.5.NF.B.5

Interpret multiplication as scaling (resizing), by:5.NF.B.4b

Find the area of a rectangle with fractional side lengths by tiling it with unit squares of the appropriate unit fraction side lengths, and show that the area is the same as would be found by multiplying the side lengths. Multiply fractional side lengths to find areas of rectangles, and represent fraction products as rectangular areas.5.NF.B.4a

Interpret the product (*a*/*b*) ×*q*as*a*parts of a partition of*q*into*b*equal parts; equivalently, as the result of a sequence of operations*a*×*q*÷*b*.*For example, use a visual fraction model to show (2/3) × 4 = 8/3, and create a story context for this equation. Do the same with (2/3) × (4/5) = 8/15. (In general, (a/b) × (c/d) = ac/bd.)*5.NF.B.4

Apply and extend previous understandings of multiplication to multiply a fraction or whole number by a fraction.

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