Radha made a picture of an aero plane with colored paper as shown in Fig 12.15. Find the total area of the paper used.



The figure of the questions is:


Sides of triangular section I = 5cm, 1cm and 5cm


Perimeter of the triangular section I = 5 + 5 + 1 = 11cm


Semi perimeter, s =   =   = 5.5cm


We use Heron’s formula to find the area of the section I,


Area of Section I =


                         =


                         =


                         =  cm2


Area of Section I = 2.48 cm2 (approx.) ~ 2.5 cm2


Length of the sides of the rectangle of section I = 6.5cm and 1 cm


Area of section II = 6.5×1 = 6.5cm2


Section III is an isosceles trapezium which is divided into three equilateral triangles each with side of 1cm each. 


Now, Area of an equilateral triangle is 


Thus, area of one equilateral triangle is 


Therefore, the area of trapezium = 3  0.43cm= 1.3 cm2


Section IV and V are congruent right angled triangles with height 1.5cm and base 6cm.


And, area of a right triangle = 


Area of region IV and V = 2  4.8 cm= 9.6 cm2


Thus, total area is 2.5 + 6.5 + 9.6 + 1.3 = 19.9 sq cm ~ 20 sq cm 

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