Decimal Operations

Adding & subtracting decimals

Stack the numbers so the decimal points line up, then add or subtract like whole numbers. Fill empty spots with zeros so every column has a digit.

When you study adding & subtracting decimals, slow down and write one example in your notebook without looking at the screen. That active step is what turns reading into learning.

Multiplying decimals

Ignore the decimal points and multiply like whole numbers. Then count the total number of decimal places in both factors and place the point that many spots from the right.

A quick way to test factors: divide the number by each candidate. If the quotient is a whole number with no remainder, you found a factor.

Every whole number has at least two factors: 1 and itself. Prime numbers have exactly those two, which is why primes are the building blocks for bigger numbers.

Why this matters

Decimal Operations shows up constantly in line up the point to add or subtract; count places to multiply. It also connects to what you will see on homework, quizzes, and the next unit in this grade.

Teachers often move fast in class. This page is here so you can pause, re-read, and practice until the idea feels familiar, not just until you have memorized a rule for one day.

Common mistakes to avoid

Rushing to the answer without writing steps. Middle-school math rewards clear work, and you catch errors earlier when steps are visible.

Mixing up similar ideas from the same topic. If two terms feel alike, make a two-column note: what is the same, what is different, and one example of each.

Key ideas from this lesson

1. Adding & subtracting decimals
2. Multiplying decimals