Using Models to Place the Decimal Point
Using models to place the decimal point is a Grade 5 math skill in enVision Mathematics, Chapter 4: Use Models and Strategies to Multiply Decimals. An area model visually confirms place value: multiplying a tenths value by another tenths value produces a hundredths result, so (a/10) × (b/10) = ab/100. This model-based approach helps students correctly place the decimal without relying solely on counting decimal places.
Key Concepts
The area model visually confirms the product's place value. Multiplying a value in the tenths place by another value in the tenths place results in a product in the hundredths place: $\frac{a}{10} \times \frac{b}{10} = \frac{ab}{100}$.
Common Questions
How does an area model help place the decimal point?
The area model shows place value visually. Tenths times tenths gives hundredths, so the area (overlap region) lands in the hundredths place, telling you where to put the decimal.
What place value is the product of two tenths?
Two tenths multiplied together give hundredths. For example, 0.4 × 0.3 = 0.12, which is in the hundredths place.
Why use a model instead of just counting decimal places?
Models build conceptual understanding of why decimal placement works, not just memorized rules. This makes it easier to catch errors and extend knowledge to new problems.
Where is using models to place the decimal point taught in enVision Grade 5?
Chapter 4: Use Models and Strategies to Multiply Decimals in enVision Mathematics, Grade 5.
Does the area model work for other decimal place values too?
Yes. Tenths × hundredths = thousandths, and hundredths × hundredths = ten-thousandths, following the same pattern.