Solve: 1.004 × 100 - Decimal Multiplication Practice

To solve this mathematical problem, let's carry out the following steps:

• Step 1: Identify the initial position of the decimal point in the number. The number is $1.004$, where the decimal point is after the first digit (1).
• Step 2: Multiply by 100. Multiplying a decimal by 100 shifts the decimal point two places to the right.
• Step 3: Move the decimal point in $1.004$ two places to the right, changing it from $1.004$ to $100.4$.

The decimal originally in the thousandths position now moves to the tenths position.

Therefore, the result of multiplying $1.004 \times 100$ is $\boxed{100.4}$.

Looking at the answer choices, we see that the correct answer corresponds to choice 3, which is $100.4$.