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A farm grew 40 quintals of paddy and 25 of ragi. It grew 35 of pulses too. A quintal is 100 kilograms. Next season every crop doubled. A list of numbers is hard to read. An average or a chart helps us read it.

Statistics means collecting numbers and reading them well. This track builds those ideas for Class 9. The farm and the class register in it are invented.

What you will learn

• One table under it all. Values with their frequencies beside them.
• The weighted average. Group size decides how much a mean counts.
• What a weight is. Weights need not be percentages.
• One bar in parts. Segments and one total, inside one bar.
• Every bar the same height. The 100% stacked bar shows shares only.
• Which chart answers. Match the question to its chart.
• Same numbers, two stories. Two honest charts can leave different impressions.
• The honest report. Five parts, each one chosen.

Quick catch-up

Six earlier lessons help here. Open any that you find hard.

• Reading a bar's scale — the gridlines show its height.
• Sharing a total out equally — the mean.
• The middle value, in order — the median.
• The value that turns up most — the mode.
• Two groups, one true mean — the bigger group counts for more.
• What a chart holds back — a percent pie has shares only.