Question

Answer it quickly please.

Answer 1

Diameter = 1m
Height = 21m

Outer surface area = 4 pie r * r
= 2 * 22/7 * 0.5/2 *0.5/2
= 11/7 * 0.5*0.5
=11/7*0.25
=2.75/7
=39.28sq.m

Cost of painting = 39.28 * 25
=rs.982

It is necessary to paint irons in order to prevent them from getting rusted.

Answer 2

(GIVEN)
diameter =1 m
height = 21 m

radius =
$\frac{ diameter}{2} \\ = \frac{1}{2}m \\ = 0.5m$

a) the outer curved surface area -
curved surface area = 2πrh
$= 2 \times \frac{22}{7} \times 0.5 \times 21 \\ = 44 \times 0.5 \times 3 \\ = 44 \times 1.5 \\ = 66{m}^{2}$
b) the cost of painting the outer surface so the pipe at rate of Rs. 25
${m}^{2}$
The total surface area = 2πr(r+h)
$= 2 \times \frac{22}{7} \times 0.5 \times (0.5 + 21) \\ = \frac{44}{7} \times 0.5 \times (21.5) \\ = \frac{473}{7} \\ = 67.57 {m}^{2}$
if the cost of painting the outer surface of pipe is Rs.25 per
${m}^{2}$
so the cost of painting 67.57
${m}^{2}$
= 67.57 X 25
=1689.25
so, the cost of painting the outer surface of the pipe is Rs. 1689.25



(but ),
cost of painting the only curved surface area of pipe
= 25 X 66
= Rs. 1650

To prevent iron from rusting it is necessary to paint the iron (pipe).