Big Idea
Decimals extend place value to parts smaller than one.
Decimals
Compare, round, add, subtract, and convert decimals.
Understand it first
Tenths
The first digit after the decimal point is tenths.
Hundredths
The second digit after the decimal point is hundredths.
Zero placeholders
2.50 has the same value as 2.5, but the zero can help align calculations.
Method Ladder
Use this same ladder every time you meet this topic.
- Line up decimal points.
- Add placeholder zeros if helpful.
- Calculate as normal by place value.
- Put the decimal point in the same aligned position.
Worked example: Calculate 3.4 + 2.75
- Write 3.4 as 3.40.
- Line up 3.40 and 2.75.
- 40 hundredths + 75 hundredths = 115 hundredths.
- 3.40 + 2.75 = 6.15.
Fix It Lab
Read these before the quiz. They are the traps that lose marks.
- Common mistakeIgnoring decimal point alignment.
- Common mistakeThinking 0.7 is smaller than 0.65 because 7 is one digit.
- Common mistakeRemoving zeros in a way that changes place value.
Top-mark challenge
Open challenge
Which is larger, 4.08 or 4.8? Explain using place value.
Write full working and one sentence explaining the method.
10-question unlock quiz
The quiz is now on separate pages. You answer one question, then the next question opens. Finish Question 10 to complete this mission.
Start Question 1