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R.1 Multiply multiples of ten using place value

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What does it mean to multiply multiples of ten?

Multiplying multiples of ten means taking numbers like 10, 20, 30, 40, 100, etc., and multiplying them together. Place value helps us understand how many zeros to include in the product.

Example:
  • 20 × 30 = 600
Note

Multiples of ten always end in a zero. This makes them easier to multiply by using place value strategies.

How do we identify multiples of ten?

A number is a multiple of ten if it ends with a zero in the ones place.

Examples:
  • 10, 20, 30, 40, 50
  • 100, 200, 300
Note

Think of multiples of ten as groups of tens. For example, 30 means 3 groups of 10.

Steps to multiply multiples of ten

To multiply multiples of ten, use place value to break the problem into two parts: multiply the basic digits, then add the zeros back.

Steps:
  • Ignore the zeros at first. Multiply the non-zero digits.
  • Count how many zeros are in the factors altogether.
  • Add that many zeros to the end of your answer.
Example:
  • 40 × 50
  • Ignore the zeros: 4 × 5 = 20
  • There are two zeros (one from each number).
  • Add the zeros: 20 → 2000
  • Answer: 40 × 50 = 2000
Note

This method works because of place value. The zeros show that the digits are shifted to the tens or hundreds place.

Using multiplication facts with multiples of ten

Basic multiplication facts (like 6 × 7 = 42) can help solve larger problems with multiples of ten.

Examples:
  • 6 × 70 = (6 × 7) × 10 = 42 × 10 = 420
  • 30 × 90 = (3 × 9) × 100 = 27 × 100 = 2700
Note

Think of the zero as a clue to multiply by ten, one hundred, or more. This connects facts you already know to bigger numbers.

Why is place value important?

Place value explains why multiplying by ten adds a zero. Each shift to the left makes the number ten times larger.

Example:
  • 4 × 10 = 40 (the digit 4 moved from the ones place to the tens place)
  • 25 × 100 = 2500 (the digits 25 moved two places left)
Note

Every zero in a multiple of ten means the number has shifted one place to the left in value.