lesson
A clear chart can still show bad data
1 · Learn
A dataset needs consistent fields, units and records. Duplicated rows, missing values and mixed units can produce misleading results even if a chart is attractive. Keep raw data unchanged while making a documented cleaned copy where appropriate.
Choose a chart for the question and show labels and scales. An apparent relationship needs interpretation; correlation alone does not establish causation.
2 · Worked example
An invented length column mixes centimetres and metres. I convert to one stated unit before calculating a mean; simply averaging the written numbers would be wrong.
3 · Your turn
Why should a blank measurement not automatically be replaced by zero?
Check your answer
Blank may mean missing, while zero is a real measured value; substitution could bias results.
4 · Apply your learning
Clean an invented table, record each justified change and compare a suitable chart before and after correction.
Adult guidance and safety
Use an approved private programming or authoring environment and fictional data. Do not install unknown software or enter personal credentials for these exercises. Trace first, then run and test where a suitable tool is available; these text examples do not themselves provide an executable assessment environment.
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Check a calculation · Year 5 onward
Use this only when your teacher or adult allows a calculator for the task. Show your thinking first. It does not replace mental or written arithmetic and does not mark your lesson answer.
Powers, roots and trigonometry · Year 7 onward
Use only when the task allows a calculator. Choose one operation at a time and record your working. Trigonometry here always uses degrees (DEG), not radians. Inverse sine, cosine and tangent return an angle, not a reciprocal. Keep exact fractions and π in answers when requested.
Approximate numerical results use up to 12 significant digits. Inverse sine returns −90° to 90°, inverse cosine 0° to 180°, and inverse tangent −90° to 90°; these are principal values, not every possible solution of a trigonometric equation.
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