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An umbrella is made by stitching 10 triangular pieces of cloth of two different colours (see Fig. 12.16), each piece measuring 20 cm, 50 cm and 50 cm. How much cloth of each colour is required for the umbrella?

Q6.    An umbrella is made by stitching 10 triangular pieces of cloth of two different colours (see Figure), each piece measuring 20 cm, 50 cm and 50 cm. How much cloth of each colour is required for the umbrella?

            

 

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The sides of the triangle are:

a = 20\ cm,\ b = 50\ cm\ and\ c =50\ cm.

So, the semi-perimeter of the triangle is given by,

s = \frac{a+b+c}{2} = \frac{20+50+50}{2} = \frac{120}{2} = 60\ cm.

Therefore, the area of the triangle can be found by using Heron's formula:

Area = \sqrt{s(s-a)(s-b)(s-c)}

            = \sqrt{60(60-20)(60-50)(60-50)}

            = \sqrt{60(40)(10)(10)} = 200\sqrt{6}\ cm^2

Now, for the 10 triangular pieces of cloths, the area will be,

= 10\times200\sqrt6 = 2000\sqrt6\ cm^2

Hence, the area of cloths of each colour will be:

= \frac{2000\sqrt6}{2} = 1000\sqrt6\ cm^2.

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