- A11
- B38
- C15
- D12
Step-by-Step Solution
The other bars give students. So the missing class has . (Averaging the neighbouring heights, , is not valid.)
Answer: D) 12
A frequency polygon (orange) has been drawn over a histogram of the time taken by 50 students to finish a puzzle. The bar for 40–50 minutes and its point on the polygon have been rubbed out. How many students took 40 to 50 minutes?
Class 9StatisticsStatistics and Probability
Key idea: Histogram vs bar graph
Both look like bars, but they differ:
**Bar graph**: For DISCRETE / categorical data (favourite colour, sport, etc.). Bars have GAPS between them. Width has no meaning.
**Histogram**: For CONTINUOUS / grouped data with class intervals. Bars TOUCH (no gaps), reflecting that the class boundaries are continuous. Bar WIDTH represents class size; HEIGHT represents frequency.
**Frequency polygon**: connect the midpoints (class marks) of the tops of histogram bars to form a line graph. Useful for comparing two distributions on the same axes.
**Key rule**: histogram bars must have no gaps; bar graph bars MUST have gaps.
**Bar graph**: For DISCRETE / categorical data (favourite colour, sport, etc.). Bars have GAPS between them. Width has no meaning.
**Histogram**: For CONTINUOUS / grouped data with class intervals. Bars TOUCH (no gaps), reflecting that the class boundaries are continuous. Bar WIDTH represents class size; HEIGHT represents frequency.
**Frequency polygon**: connect the midpoints (class marks) of the tops of histogram bars to form a line graph. Useful for comparing two distributions on the same axes.
**Key rule**: histogram bars must have no gaps; bar graph bars MUST have gaps.
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