🏰 Number Kingdom · Significant figures
Round decimals to a chosen number of significant figures, including very small values. In this lesson, focus on significant figures describe the important digits in a value.
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Round decimals to a chosen number of significant figures, including very small values. In this lesson, focus on significant figures describe the important digits in a value.
Significant figures describe the important digits in a value. Counting starts at the first non-zero digit, not automatically at the decimal point, and zeros inside or after significant digits may matter. For rounding decimals to significant figures, the final written answer should make that exact relationship visible rather than hiding it inside an unexplained result.
Rounding decimals to significant figures: Significant figures describe the important digits in a value. Read the rounded answer back at the original scale and count the significant digits again. Keep the rounding decimals to significant figures representation visible until the final line.
Highlight each digit from the first non-zero digit and classify zeros as leading placeholders or significant information. Use the model to explain one change you notice while working on rounding decimals to significant figures.
Read the rounded answer back at the original scale and count the significant digits again. Write that check beside the final rounding decimals to significant figures answer.
First significant figure = first non-zero digit.
Visual / interactive
Highlight each digit from the first non-zero digit and classify zeros as leading placeholders or significant information. Use the model to explain one change you notice while working on rounding decimals to significant figures.
Worked examples
Understand the idea with small numbers, one representation and one clear step.
Use the standard Year 8 method with mixed examples and normal wording.
Handle multi-step or less familiar questions and explain choices.
Solve a worded question, show reasoning, check accuracy and write a final sentence.
Given information: Rounding decimals to significant figures — Round 0.0324 to 2 significant figures. Method choice: count significant figures from the first non-zero digit, then inspect the next digit. Calculation or reasoning: The first two significant digits are 3 and 2. The next digit is 4. Since 4 is less than 5, the second significant digit stays the same. Final answer: 0.032. Check: 0.032 has 2 significant figures.
Given information: Rounding decimals to significant figures — Round 0.031414 to 3 significant figures. Method choice: count significant figures from the first non-zero digit, then inspect the next digit. Calculation or reasoning: The first three significant digits are 3, 1 and 4. The next digit is 1. Since 1 is less than 5, the third significant digit stays the same. Final answer: 0.0314. Check: 0.0314 has 3 significant figures.
Check: Keep place-value zeros needed to show the size of the number.
Given information: Rounding decimals to significant figures — Round 0.03139 to 2 significant figures. Method choice: count significant figures from the first non-zero digit, then inspect the next digit. Calculation or reasoning: The first two significant digits are 3 and 1. The next digit is 3. Since 3 is less than 5, the second significant digit stays the same. Final answer: 0.031. Check: 0.031 has 2 significant figures.
Try explaining why each step works before checking the answer.
Given information: Rounding decimals to significant figures — Round 0.03124 to 3 significant figures. Method choice: count significant figures from the first non-zero digit, then inspect the next digit. Calculation or reasoning: The first three significant digits are 3, 1 and 2. The next digit is 4. Since 4 is less than 5, the third significant digit stays the same. Final answer: 0.0312. Check: 0.0312 has 3 significant figures.
Read the rounded answer back at the original scale and count the significant digits again. Write that check beside the final rounding decimals to significant figures answer.
Create a rounding decimals to significant figures problem with a tempting incorrect answer. Solve it, apply the check, and explain exactly where the incorrect method breaks down.
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Use digit hunt controls to solve three checked rounding decimals to significant figures rounds. Solve at least two of three marked rounds and use feedback to correct any error.
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Rounding decimals to significant figures: Significant figures describe the important digits in a value. Read the rounded answer back at the original scale and count the significant digits again. Keep the rounding decimals to significant figures representation visible until the final line.
Tap to mark reviewedsignificant figure · first non-zero digit · leading zero · placeholder zero · accuracy · rounding · decimals
Tap to mark reviewedLocate the first non-zero digit. Count significant digits from left to right. If rounding, circle the final kept digit. Use the next digit to decide whether to round and keep place-value zeros where needed. Record the check explicitly for rounding decimals to significant figures.
Tap to mark reviewedFirst significant figure = first non-zero digit.
Tap to mark reviewedGiven information: Rounding decimals to significant figures — Round 0.0324 to 2 significant figures. Method choice: count significant figures from the first non-zero digit, then inspect the next digit. Calculation or reasoning: The first two significant digits are 3 and 2. The next digit is 4. Since 4 is less than 5, the second significant digit stays the same. Final answer: 0.032. Check: 0.032 has 2 significant figures.
Tap to mark reviewedGiven information: Rounding decimals to significant figures — Round 0.031414 to 3 significant figures. Method choice: count significant figures from the first non-zero digit, then inspect the next digit. Calculation or reasoning: The first three significant digits are 3, 1 and 4. The next digit is 1. Since 1 is less than 5, the third significant digit stays the same. Final answer: 0.0314. Check: 0.0314 has 3 significant figures.
Tap to mark reviewedGiven information: Rounding decimals to significant figures — Round 0.03139 to 2 significant figures. Method choice: count significant figures from the first non-zero digit, then inspect the next digit. Calculation or reasoning: The first two significant digits are 3 and 1. The next digit is 3. Since 3 is less than 5, the second significant digit stays the same. Final answer: 0.031. Check: 0.031 has 2 significant figures.
Tap to mark reviewedGiven information: Rounding decimals to significant figures — Round 0.03124 to 3 significant figures. Method choice: count significant figures from the first non-zero digit, then inspect the next digit. Calculation or reasoning: The first three significant digits are 3, 1 and 2. The next digit is 4. Since 4 is less than 5, the third significant digit stays the same. Final answer: 0.0312. Check: 0.0312 has 3 significant figures.
Tap to mark reviewedCounting leading zeros as significant. This is a key trap when answering rounding decimals to significant figures questions.
Tap to mark reviewedFor rounding decimals to significant figures, show the key representation before the final calculation. Use this final check: Read the rounded answer back at the original scale and count the significant digits again.
Tap to mark reviewedScientific measurements, Population estimates
Tap to mark reviewedI can explain rounding decimals to significant figures, use the method, check for mistakes, and answer an exam-style question.
Tap to mark reviewedI’m Stuck
Use this whenever a question feels confusing. Nothing here is locked.
Rounding decimals to significant figures: Significant figures describe the important digits in a value. Read the rounded answer back at the original scale and count the significant digits again. Keep the rounding decimals to significant figures representation visible until the final line.
Think of rounding decimals to significant figures as a careful model: make the important values visible, change one thing at a time, and use the check to prove the answer fits.
Start by naming the given information and the exact result required for rounding decimals to significant figures.
Locate the first non-zero digit.
Given information: Rounding decimals to significant figures — Round 0.0324 to 2 significant figures. Method choice: count significant figures from the first non-zero digit, then inspect the next digit. Calculation or reasoning: The first two significant digits are 3 and 2. The next digit is 4. Since 4 is less than 5, the second significant digit stays the same. Final answer: 0.032. Check: 0.032 has 2 significant figures.
Method: Locate the first non-zero digit. → Count significant digits from left to right. → If rounding, circle the final kept digit. → Use the next digit to decide whether to round and keep place-value zeros where needed. Record the check explicitly for rounding decimals to significant figures.
Counting leading zeros as significant. This is a key trap when answering rounding decimals to significant figures questions.
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