Class 9 Frequency Polygons — practice questions with answers
Statistics and Probability · 5 sample questions from the school syllabus. Try each one, then open the answer and the worked solution.
1. In a frequency polygon, each point is plotted using which value on the horizontal axis?
AClass mark (mid-point) of the class
BLower class limit
CUpper class limit
DClass size
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Answer: A) Class mark (mid-point) of the class
A frequency polygon is drawn by plotting the class mark (mid-point) of each class against its frequency.
2. A frequency polygon meets the x-axis at both ends only when:
AImaginary classes of zero frequency are added at both ends
BThe frequencies are all equal
CThe class size is 1
DThe data is continuous
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Answer: A) Imaginary classes of zero frequency are added at both ends
Adding a zero-frequency class before the first and after the last brings the polygon down to the x-axis at both ends.
3. While drawing a frequency polygon over a histogram, how many points are joined if the histogram has 6 bars (without closing at the ends)?
A5
B6
C7
D12
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Answer: B) 6
One mid-point per bar top is plotted, so 6 bars give 6 points (closing the polygon would add 2 more zero-frequency points).
4. The marks of 40 students of Class 9 in Kolkata are grouped (class size 10). The frequency polygon passes through (5, 0), (15, 6), (25, 10), (35, 14), (45, 8), (55, 2), (65, 0). What is the frequency of the class 40-50?
A16
B7
C8
D9
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Answer: C) 8
Class 40-50 has class mark 45. The plotted point (45, 8) gives a frequency of 8.
5. A frequency polygon has the symmetric points (10, 2), (20, 8), (30, 15), (40, 8), (50, 2). Because the polygon is symmetric about a vertical line, where (which class mark) does that line of symmetry lie?
A33
B30
C60
D27
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Answer: B) 30
The frequencies are symmetric (2, 8, 15, 8, 2) about the middle point at class mark 30, so the axis of symmetry is x = 30.