Question

18. In the marriage of Raj's brother Mahesh, a conical tent is made by stitching 12 triangular pieces of
cloth of two different colours red and white alternately, each piece measuring 10 cm, 20 cm and 20
cm,
20cm
ho

(v) Find the total length of triangular pieces of white colour.
(a) 200 cm
(b) 300 cm (c) 350 cm (d) 400 cm​

Answer 1

Correct Question -

In the marriage of Raj's brother Mahesh, a conical tent is made by stitching 12 triangular pieces of cloth of two different colours red and white alternatively, each piece measuring 10cm,20cm and 20cm .

Find the total length of triangular pieces of white colour.

(a) 200 cm

(b) 300 cm

(c) 350 cm

(d) 400 cm

Solution :

Let us find the area of one of the triangular piece first .

For this , the sides are 10 cm , 20cm and 20 cm in length .

Semiperimeter -

> ( a + b + c )/2

> 25 cm .

Area :

> √s(s-a)(s-b)(s-c)

> √ 25 × ( 25 - 10)( 25 - 20)( 25 - 20)

> √ 25 × 15 × 5 × 5

> 25√15

The perimeter of the triangular piece -

> 10 cm + 20 cm + 20 cm

> 50 cm.

Perimeter of 6 pieces ( As there are two colours white and rec )

> 50 × 6

> 300 cm .

Hence Option (B) is the required answer .

________________________________

Answer 2

Answer:

Given :-

Side of triangle = 10 cm, 20 cm and 20 cm

To Find :-

Total length

Area

Solution :-

Area = a + b + c/2 then, √s(s-a)(s-b)(s-c)

Now,

Semiperimeter = 10 + 20 + 20/2

Semiperimeter = 30 + 20/2

Semiperimeter = 50/2

Semiperimeter = 25 cm

Now,

Area = √25(25 - 10)(25 - 20)(25 - 20)

Area = √25(15)(5)(5)

Area = 96.824 cm²

Now,

Perimeter = a + b + c

Perimeter = 10 + 20 + 20

Perimeter = 50 cm

Now,

Length of 6 pieces = 6 × Perimeter of one piece

Length = 6 × 50

Length = 300 cm

Therefore,

${ \large{ \fbox{ \red{ \underline{Option B \checkmark}}}}}$