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Assertion (A): The perimeter of a square of side 10 cm is 40 cm. Reason (R): Perimeter of a square = 4 × side. Choose the correct option.

Class 6MensurationMensuration
  • ABoth A and R are true, and R is the correct explanation of A.
  • BBoth A and R are true, but R is not the correct explanation of A.
  • CA is true but R is false.
  • DA is false but R is true.

Step-by-Step Solution

Perimeter of a square = 4 × side = cm, so A is true. R states the correct formula and is exactly the reason A holds, so R correctly explains A.
Answer: A) Both A and R are true, and R is the correct explanation of A.

Key idea: Perimeter shortcuts for special shapes

**Rectangle**: opposite sides are equal, so perimeter = l + b + l + b = 2(l + b).

**Square**: all four sides equal, so perimeter = 4 × s.

**Equilateral triangle**: all three sides equal, perimeter = 3 × s.

**Regular polygon with n sides of length s**: perimeter = n × s.

These shortcuts are just 'add the sides' written shorter.

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