A relatively easy four mark question from the chapter Statistics. Two steps to arrive at the answer. The calculation is also easy for this question.
Question 30A: The mean of the following distribution is 18. Find the frequency f of the class 19 – 21.
Class | 11 - 13 | 13 - 15 | 15 - 17 | 17 - 19 | 19 - 21 | 21 - 23 | 23 - 25 |
---|---|---|---|---|---|---|---|
Frequency | 3 | 6 | 9 | 13 | f | 5 | 4 |
Class | Frequency fi | Class Mean xi | fixi |
---|---|---|---|
11 - 13 | 3 | 12 | 36 |
13 - 15 | 6 | 14 | 84 |
15 - 17 | 9 | 16 | 144 |
17 - 19 | 13 | 18 | 234 |
19 - 21 | f | 20 | 20f |
21 - 23 | 5 | 22 | 110 |
23 - 25 | 4 | 24 | 96 |
Σfi = 40 + f
Σfixi = (704 + 20f)
Mean x = \\frac{Σf_i x_i}{Σf_i})
18 = \\frac{704 + 20f}{40 + f})
18(40 + f) = 704 + 20f
720 + 18f = 704 + 20f
16 = 2f
f = 8
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1. Section A | 2018 CBSE Class 10 Maths 1 Mark Questions 1 to 6
2. Section B | 2018 CBSE Class 10 Maths 2 Mark Question 7 | Real Numbers - Irrational Numbers
3. Section B | 2018 CBSE Class 10 Maths 2 Mark Question 8 | Linear Equations in 2 variables
4. Section B | 2018 CBSE Class 10 Maths 2 Mark Question 9 | Sum of Arithmetic Progressions
5. Section B | 2018 CBSE Class 10 Maths 2 Mark Question 10 | Coordinate Geometry Section Formula
6. Section B | 2018 CBSE Class 10 Maths 2 Mark Question 11 | Probability of Rolling 2 dice
7. Section B | 2018 CBSE Class 10 Maths 2 Mark Question 12 | Probability of selecting numbers
8. Section C | 2018 CBSE Class 10 Maths 3 Mark Question 13 | Real Numbers - LCM & HCF
9. Section C | 2018 CBSE Class 10 Maths 3 Mark Question 14 | Polynomial Factorization
10. Section C | 2018 CBSE Class 10 Maths 3 Mark Question 15A | Coordinate Geometry - Parallelogram
11. Section C | 2018 CBSE Class 10 Maths 3 Mark Question 15B | Coordinate Geometry - Area of Triangles
12. Section C | 2018 CBSE Class 10 Maths 3 Mark Question 16 | Quadratic Equations - Speed Time Distance
13. Section C | 2018 CBSE Class 10 Maths 3 Mark Question 17 | Similar & Congruent Triangles
14. Section C | 2018 CBSE Class 10 Maths 3 Mark Question 19 | Trigonometric Ratios
15. Section C | 2018 CBSE Class 10 Maths 3 Mark Question 20 | Areas related to circles - sector area
16. Section C | 2018 CBSE Class 10 Maths 3 Mark Question 21 | Surface Areas & Volumes - Cylinder, hemisphere and cone
17. Section C | 2018 CBSE Class 10 Maths 3 Mark Question 22 | Statistics - Median
18. Section D | 2018 CBSE Class 10 Maths 4 Mark Question 23 | Quadratic Equations _ Speed Distance Time
19. Section D | 2018 CBSE Class 10 Maths 4 Mark Question 24 | Arithmetic Progressions
20. Section D | 2018 CBSE Class 10 Maths 4 Mark Question 25A | Equilateral & Right Triangles and Congruence
21. Section D | 2018 CBSE Class 10 Maths 4 Mark Question 25B | Pythagoram Theorem Proof
22. Section D | 2018 CBSE Class 10 Maths 4 Mark Question 27 | Trigonometric Ratios & Identities
23. Section D | 2018 CBSE Class 10 Maths 4 Mark Question 28 | Surface Area of Frustum
24. Section D | 2018 CBSE Class 10 Maths 4 Mark Question 29 | Applications of Trigonometry - Heights & Distances
25. Section D | 2018 CBSE Class 10 Maths 4 Mark Question 30 | Statistics - 2 Alternatives
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