Example

Multiplying (3.9)(4.075)(-3.9)(4.075)

Multiply (3.9)(4.075)(-3.9)(4.075) by applying the four-step decimal multiplication procedure:

  1. Determine the sign: The factors have different signs (3.9-3.9 is negative and 4.0754.075 is positive), so the product will be negative.
  2. Write in vertical format and multiply as whole numbers: Align 4.0754.075 and 3.93.9 on the right (ignoring decimal points). Multiply digit by digit: 4075×9=36,6754075 \times 9 = 36{,}675 and 4075×3=12,2254075 \times 3 = 12{,}225 (shifted one place left). Adding the partial products gives 36,675+122,250=158,92536{,}675 + 122{,}250 = 158{,}925.
  3. Place the decimal point: Count decimal places in each factor — 3.93.9 has 11 decimal place and 4.0754.075 has 33 decimal places, for a total of 1+3=41 + 3 = 4 decimal places. Starting from the rightmost digit of 158925158925, move 44 places to the left to get 15.892515.8925.
  4. Apply the sign: Since the factors have different signs, the product is negative.

The result is (3.9)(4.075)=15.8925(-3.9)(4.075) = -15.8925.

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Updated 2026-05-02

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