Question

plz give me answer of question 12&13

Answer 1

$Question:$

The inner and outer radii of a cylindrical pipe are 4 cm and 5 cm respectively. Find the cross-sectional area of the pipe.Use $\pi =3.14$.

$Solution:$

Given :

• R = 5 cm
• r = 4 cm.

We know that , Area of cross-section of the pipe :

$\pi (R^{2}- r^{2} )\\\\= \pi (5^2-4^2)\\\\=\pi (25-16)\\\\=\pi *9=3.14*9=28.26 square.cm$

$Question:$

From a rectangular piece of metal sheet of length and breadth 1.60 m and 80 cm respectively. 3 circular sheets of 20 cm radius are cut out. What area of metal is left ? Use $\pi =3.14$.

$Solution:$

Given :

• Length = 160 cm.
• Breadth = 80 cm.
• Radius of each circular metal = 20 cm.

We know that ,

Area of rectangular sheet = Length × Breadth

So,

Area of metal sheet = 160 × 80 = 12800 cm².

• Area of circle = π r²

Area of three identical circular metal sheet = 3 (3.14×20×20)

                                                                       = 3768 cm².

Area of remaining sheet = Δ of metal sheet - Δof 3 circular sheet

                                         = 12800 - 3768 = 9032 cm².

Thanks..