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AA.2 Use exponents to divide decimals by powers of ten

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What does it mean to divide decimals by powers of ten?

Dividing decimals by powers of ten means using exponents to understand how a number changes when it is divided by 10, 100, 1,000, or other powers of ten. A power of ten is any number that can be written as 10n, where n is the exponent.

Example:
  • 101 = 10
  • 102 = 100
  • 103 = 1,000
Note

The exponent tells you how many zeros the power of ten has.

What happens when you divide by a power of ten?

When you divide a decimal by a power of ten, the digits in the number move to the right. Each place-value shift is controlled by the exponent.

Example:
  • 4.5 ÷ 10 = 0.45 (digits shift 1 place right)
  • 4.5 ÷ 100 = 0.045 (digits shift 2 places right)
  • 4.5 ÷ 1,000 = 0.0045 (digits shift 3 places right)
Note

Dividing by 10n always shifts the digits n places right, not the decimal point.

Using exponents to describe division

We use exponents to write powers of ten in a shorter way. This helps us describe how much a number will change when it is divided.

Example:
  • 7.2 ÷ 102 = 0.072
  • 9.84 ÷ 103 = 0.00984
  • 0.56 ÷ 101 = 0.056
Note

Think of the exponent as a “shift counter” that tells you how far the digits move.

Dividing whole numbers and decimals using powers of ten

The same rules work whether the number is a whole number, a decimal, or a mixed decimal. Dividing by powers of ten always reduces the value by shifting digits right.

Examples:
  • 600 ÷ 102 = 6
  • 83 ÷ 101 = 8.3
  • 0.305 ÷ 103 = 0.000305
Note

If zeros appear in front of the number, that is normal. They show the place-value shift correctly.

Modeling division with place-value reasoning

Place-value reasoning helps explain why digits shift. Each division by 10 reduces a digit’s value to one-tenth of what it was before.

Example:
  • In 3.6 ÷ 10, the 3 moves from the ones to the tenths, and the 6 moves from the tenths to the hundredths → 0.36
  • In 3.6 ÷ 100, each digit moves two places right → 0.036
Note

Dividing never changes the order of digits—only their place values.

Using patterns to check your division

Patterns in the number help confirm your answer. The quotient should always be smaller when you divide by a power of ten.

Examples:
  • 45 ÷ 10 = 4.5 (smaller)
  • 45 ÷ 100 = 0.45 (even smaller)
  • 45 ÷ 1,000 = 0.045 (smallest)
Note

If your quotient becomes larger, check your place-value shifts again.