What is the first step in the decimal addition/subtraction rule?

The first step in the decimal addition or subtraction process is to line up the decimals. This is crucial because each digit represents a different place value (ones, tenths, hundredths, etc.), and proper alignment ensures that you are adding or subtracting corresponding values accurately. When the decimal points are lined up vertically, it guarantees that you correctly add or subtract digits in each place value, leading to an accurate final result. If the decimals are not aligned, it can lead to mistakes in the calculations and result in incorrect answers.

Other actions, such as aligning whole numbers or converting to fractions, are either secondary steps or not aligned with the specific rules for decimal operations. Simplifying the numbers may also be a technique in some contexts but does not apply directly to decimal addition or subtraction as the initial step.