- A150
- B120
- C540
- D135
Step-by-Step Solution
Read the four bar heights and average them: units. The total 540 is the sum, not the mean.
Answer: D) 135
A bar graph shows the units of a product sold each month. The bars read Jan 120, Feb 150, Mar 90 and Apr 180. What is the mean number of units sold per month?
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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