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Arjun draws a house: a square of side l with an equilateral triangle of side l on top. The thick line is the outline (the dashed side is inside). What is the perimeter of the outline, and its value when l = 7 cm?

Class 6AlgebraAlgebra
  • A7l; 49 cm
  • B5l; 35 cm
  • C6l; 42 cm
  • D4l; 28 cm

Step-by-Step Solution

The outline has 3 sides of the square and 2 sides of the triangle: . (The shared dashed side is not on the outline.) For cm.
Answer: B) 5l; 35 cm

Key idea: Evaluating an expression

To evaluate an expression, **substitute** a value for the variable and compute. If , then becomes . The same expression with gives . Practise substituting — it is the bridge between an algebraic expression and a real number.

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