NCERT Solutions for Class 10 Maths Chapter 12
Important NCERT Questions
Areas Related To Circles Class,
NCERT Books for Session 2022-2023
CBSE Board and UP Board Others state Board
EXERCISE 12.2
Page No:231
Questions No:13
A round table cover has six equal designs as shown in If the radius of the cover is 28 cm, find the cost of making the designs at the rate of ` 0.35 per cm2. (Use √3 = 1.7)
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since the circle is divided into 6 equal parts , therefore each sector will make an angle of 60 degrees with the centre
360/6=60degrees .
now if we find the area of one sector we can easily find the total area of all sector by multiplying 6 in the area of sector of 1 part using the formula
then the cost of 1msquare is already given so we can find the cost of making designs on 6 parts easily
6 design of table cover = 6 sectors of circle
Therefore, angle of each sector = 360°/6 = 60°
In △OAB,
∠OAB = ∠OBA [Because OA = OB]
∠AOB = 60°
∠0AB + ∠OBA + ∠AOB = 180°
2∠0AB = 180° – 60° = 120°
∠0AB = 60°
Similarly, △OAB is an equilateral triangle.
Area of sector OAPB
60°/360° × πr²
= 1/6 × π(28)²
= 1/6 × 28 × 28
= 1232/3 cm²
Area of equilateral triangle OAB
= √3/4(28)² = 196√3
= 196 x 1.7 = 333.2 cm²
Area of segment
= Area of sector OAPB – area of equilateral triangle OAB
= (1232/3 – 333.2) cm²
Area of 6 designs of table cover
= 6 x (1232/2 – 333.2) cm²
= (2464 – 1999.2) cm² = 464.8 cm²
Cost of making 1 cm² design = ₹ 0.35
Therefore, the cost of making 464.8 cm² design = ₹ 0.35 × 464.8 = ₹ 162.68