Ch 12 covers collection, presentation, and analysis of data. Students learn to construct frequency distributions, draw histograms and frequency polygons, and calculate measures of central tendency.
Data can be primary (collected directly) or secondary (from published sources). Raw data is organised into a frequency distribution table with class intervals and frequencies. Use tally marks for counting.
Histograms represent grouped continuous data with bars (no gaps). Frequency polygons connect midpoints of histogram bars. For unequal class widths, adjust bar heights using frequency density.
Mean of grouped data: x̄ = Σ(f × x)/Σf, where x = class mark. Mode is the observation/class with highest frequency. Median is the middle value of ordered data. For ungrouped data: if n is odd, median = middle value; if n is even, median = average of two middle values.
Download: https://ncert.nic.in/textbook/pdf/iemh112.pdf | Complete book: https://ncert.nic.in/textbook/pdf/iemh1ps.zip
Histograms are for continuous grouped data (bars touch). Bar graphs are for discrete/categorical data (bars have gaps). Histograms show frequency distribution; bar graphs compare categories.
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