Decimal Multiplication

0.3 × 0.4 = 0.12: count decimal places in factors (1 + 1 = 2), that's places in product. The rule looks magical but follows from fraction equivalents. Indirect aim: scientific notation, preparation for algebraic decimal operations.

• Framework: Montessori
• Unit: Mathematics
• Learning area: Decimal Fractions
• Level: Ages 8-10

Objectives

• Multiply decimals: 0.3 × 0.4 = 0.12
• Count decimal places in factors = places in product
• Use Checkerboard with decimal extension
• Apply to real money problems

Materials

• Decimal Checkerboard or grid
• Decimal Fraction Board
• Problem slips
• Calculator for verification

Instructions

1. Write 0.3 × 0.4. 2. Convert: 3/10 × 4/10 = 12/100 = 0.12. 3. Note: 1+1 = 2 decimal places in answer. 4. Verify: 3 × 4 = 12; place decimal 2 places left = 0.12. 5. Rule: count decimal places in both factors, that's decimal places in product. 6. Compute 2.5 × 0.3 = 0.75. 7. Apply: buy 2.5 kg at $0.30/kg = $0.75. 8. Verify with calculator.

Educator tip

Money problems anchor this. The 'decimal places add' rule is easier to see with groceries than with pure math.

Assessment

Observe correct multiplication, decimal placement, and real-world application.

More from Mathematics

• Decimal Division
• Perimeter — Various Polygons
• Angles and Protractor Use
• Ratio and Proportion
• Integer Operations — Signed Number Arithmetic
• Word Problems — Distance, Rate, Time
• Geometry Chart 1 — Basic Figures
• Congruence and Similarity