Last updated at March 3, 2017 by Teachoo

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Example 6 A corn cob (see Fig. ), shaped somewhat like a cone, has the radius of its broadest end as 2.1 cm and length (height) as 20 cm. If each 1 cm2 of the surface of the cob carries an average of four grains, find how many grains you would find on the entire cob. We know that grains are on the curved surface Area First we find the area of corn cob which is in the form of a cone. Curved Surface Area of corn cob = πrl r = 2.1 cm, h = 20cm Let slant height be l We know that l2 = h2 + r2 l2 = "(20)2 + (2.1)2" l2 = "400 + 4.4" 1 l2 = "40" 4.41 l = √("40" 4.41) l = √("20.112" ) l = 20.11 cm Now, Area of corn cob = Curved Surface area of cone = πrl = 22/7 × 2.1 × 20.11 cm2 = 132.726 cm2 = 132.73 cm2 (approx.) Number of grains on 1 cm2 of the surface of corn cob = 4 Number of grains on 132.73 cm2 of the surface of corn cob = 132.73 × 4 = 530.92 = 531 (approx) So, there would be approximately 531 grains of corn on the cob.

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Example 6 Important You are here

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Surface Area and Volume Formulas Important

Class 9

Important Questions for Exam - Class 9

- Chapter 1 Class 9 Number Systems
- Chapter 2 Class 9 Polynomials
- Chapter 3 Class 9 Coordinate Geometry
- Chapter 4 Class 9 Linear Equations in Two Variables
- Chapter 5 Class 9 Introduction to Euclid's Geometry
- Chapter 6 Class 9 Lines and Angles
- Chapter 7 Class 9 Triangles
- Chapter 8 Class 9 Quadrilaterals
- Chapter 9 Class 9 Areas of parallelograms and Triangles
- Chapter 10 Class 9 Circles
- Chapter 11 Class 9 Constructions
- Chapter 12 Class 9 Herons Formula
- Chapter 13 Class 9 Surface Areas and Volumes
- Chapter 14 Class 9 Statistics
- Chapter 15 Class 9 Probability

About the Author

Davneet Singh

Davneet Singh is a graduate from Indian Institute of Technology, Kanpur. He provides courses for Mathematics from Class 9 to 12. You can ask questions here.