Question

A cylindrical flask of base perimeter 44 cm and height 15 cm needs to be coloured. If the cost of colouring 1 cm${}^2$ area is ₹ 0.1, then find the total cost of colouring the flask.

• A. ₹ 96.8
• B. ₹ 99.8
• C. ₹ 101.8
• D. ₹ 96

Answer 1

The correct option is A ₹ 96.8

Given, perimeter of the base = 44 cm
We know, perimeter of base = perimeter of circle = $2\pi r$ = 154 cm
Therefore, $r=\frac{154\times 7}{2\times 22}=7cm$

The cylindrical flask is in the shape of cylinder and we know that the total surface area of cylinder of radius 'r' and height 'h' is given by $2\pi r(r+h).$
Therefore, the total surface area of the flask
$=2\pi r(r+h)=2\times \frac{22}{7}\times 7\times (7+15)=44\times 22=968c{m}^2$
Given, the cost of colouring 1 cm${}^2$ area is ₹ 0.1.
$\therefore$ Cost of colouring an area of 968 cm${}^2$
$=968\times 0.1=₹96.8$