A triangular road sign has sides 45 cm, 45 cm and 38 cm. What is its perimeter?

Class 6MensurationMensuration

A83 cm
B90 cm
C128 cm
D133 cm

Step-by-Step Solution

Add all three sides: 45 + 45 + 38 = 128 cm. 90 cm counts only the two equal sides and 83 cm counts one equal side with the base — every side must be included exactly once, even when two of them are the same length.

Answer: C) 128 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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