**A metal pipe is 77 cm long. The inner diameter of a cross section is 4 cm, the outer diameter being 4.4 cm . Find its****(i) inner curved surface area,**** (ii) outer curved surface area,**** (iii) total surface area.**

**Solution (i)**

Inner diameter of cross-section **cm**

Inner radius of cross-section **cm**

Height of pipe **cm**

Inner curved surface area of metal pipe

**Solution (ii)**

Outer diameter of cross-section **cm**

Outer radius of cross-section **cm**

Height of pipe **cm**

Outer curved surface area of metal pipe

**Solution (iii)**

It is very important to understand in this part that we are going to add to inner curved surface area and outer curved surface area to get total surface area. So, the question is from where did came up?

We are going to understand this with the help of diagram. We can see that area of portion shaded in blue is also part of the pipe.

Area of upper shaded portion would be = Area of outer circle -Area of inner circle

Area of total shaded portion would be

Therefore,** total surface area of pipe** =Inner curved surface area of pipe + Outer curved surface area of pipe+