In this Grade 5 Eureka Math lesson from Chapter 5, students learn to multiply decimal fractions by single-digit whole numbers by reasoning about place value units and using estimation to confirm correct decimal point placement. Using area models and vertical multiplication, students work through problems such as 3.1 × 4 and 5.1 × 6, converting decimals to unit form (tenths, hundredths) to find and verify products. The lesson builds toward abstract multiplication fluency by connecting digit patterns across whole-number and decimal multiplication sentences.
Section 1
Confirming Decimal Placement with Estimation
To estimate the product of a decimal and a whole number, round the decimal to the nearest whole number and multiply. The actual product will be approximately equal to the estimated product, which helps confirm the correct placement of the decimal point.
Section 2
Decimal Multiplication with Unit Form
To multiply a decimal by a whole number, convert the decimal to its smallest unit form (e.g., becomes 25 tenths). Multiply the resulting whole number by the multiplier. The product will be in that same unit, which can then be converted back to standard decimal form.
Expand to review the lesson summary and core properties.
Section 1
Confirming Decimal Placement with Estimation
To estimate the product of a decimal and a whole number, round the decimal to the nearest whole number and multiply. The actual product will be approximately equal to the estimated product, which helps confirm the correct placement of the decimal point.
Section 2
Decimal Multiplication with Unit Form
To multiply a decimal by a whole number, convert the decimal to its smallest unit form (e.g., becomes 25 tenths). Multiply the resulting whole number by the multiplier. The product will be in that same unit, which can then be converted back to standard decimal form.