Circle is a closed curved shape where all points are equally distant from the center. In SSC CGL, circle questions appear in almost every paper, focusing mainly on area and circumference calculations. Understanding these basics can fetch you 2-3 marks guaranteed.
Radius (r): Distance from center to any point on circle
Diameter (d): Twice the radius, d = 2r
Circumference: Total boundary length of circle
Area: Space enclosed within the circle
SSC CGL typically asks direct formula applications, finding one parameter when another is given, and combined problems involving cost calculations. Questions often involve practical scenarios like wire bending, garden fencing, or circular plots.
#1 - Quick Area from Circumference: When circumference is given, use this direct formula: Area = C²/(4π) This saves time by avoiding the step of finding radius first. Shortcut Trick #2 - Ratio Method: If radius changes by factor k, then circumference changes by factor k, but area changes by factor k². This helps in comparison problems. Shortcut Trick #3 - Approximation Technique: For quick calculations, use π ≈ 22/7 for fractions and π ≈ 3.14 for decimals.
Find radius using C = 2πr 44 = 2 × (22/7) × r 44 = (44/7) × r r = 44 × 7/44 = 7 meters
Calculate area Area = πr² = (22/7) × 7² = (22/7) × 49 = 22 × 7 = 154 sq meters Alternative using shortcut: Area = C²/(4π) = 44²/(4 × 22/7) = 1936/(88/7) = 1936 × 7/88 = 154 sq meters Worked Example 2: A wire of length 88 cm is bent to form a circle. If the same wire is bent to form a square, what is the ratio of areas?
Circle area Circumference = 88 cm, so radius = 88/(2π) = 88/(2 × 22/7) = 14 cm Circle area = πr² = (22/7) × 14² = (22/7) × 196 = 616 sq cm
Square area Perimeter = 88 cm, so each side = 88/4 = 22 cm Square area = 22² = 484 sq cm
Ratio = Circle area : Square area = 616 : 484 = 14 : 11 Most Common Trap - The #1 Mistake: Students confuse diameter with radius. When a problem states 'circle of 14 cm', always check if it refers to radius or diameter. This single mistake can cost you the entire question. Always read twice and identify clearly whether the given measurement is radius or diameter. Another frequent error is forgetting to square the radius in area calculations. Students often write Area = πr instead of πr². Practice writing the complete formula every time to
13graded MCQs · easy to hard · full solution & trap analysis