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A triangular kite has a perimeter of 40 cm. Two of its sides are 13 cm and 15 cm. How long is the third side?

Class 6MensurationMensuration
  • A12 cm
  • B14 cm
  • C28 cm
  • D68 cm

Step-by-Step Solution

Third side = perimeter − (sum of the other two) = 40 − (13 + 15) = 40 − 28 = 12 cm. 28 cm is only the sum of the two given sides, and 68 cm comes from adding all three numbers instead of subtracting.
Answer: A) 12 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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