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An isosceles triangular pennant has a perimeter of 74 cm and a base of 20 cm. How long is each of its two equal sides?

Class 6MensurationMensuration
  • A24 cm
  • B27 cm
  • C37 cm
  • D54 cm

Step-by-Step Solution

Take the base away first: 74 − 20 = 54 cm is shared between the two equal sides, so each one is 54 ÷ 2 = 27 cm. Stopping at 54 cm gives both sides together, not one. 37 cm is half the whole perimeter, which ignores the base completely.
Answer: B) 27 cm

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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