Question

The inner diameter of a well is 4.20 metre and
its depth is 10 metre. Find the inner surface area
of the well. Find the cost of plastering it from
inside at the rate Rs: 52 per sq. m.​

Answer 1

Given :-

Inner diameter of a well is 4.20 m

And height = 10m

To find :-

The Inner surface area

and the cost of plastering

Now

A T.Q

$\boxed{\sf{C.S.A\:of\:well=2\pi r h}}$

Now first find the radius

$\sf\implies Radius =\dfrac{Diameter}{2}\\ \\ \sf\implies Radius= \cancel{\dfrac{4.20}{2}}\\ \\ \sf\implies{\red{ Radius= 2.1m}}$

So the C.S.A

$\sf\implies C.S.A=2 \pi r h\\ \\ \sf\implies C.S.A=2\times \dfrac{22}{7}\times 2.1\times 10\\ \\ \sf\implies C.S.A= \dfrac{2\times 22\times 2.1\times 10}{7}\\ \\ \sf\implies C.S.A=\dfrac{44\times 21}{7}\\ \\ \sf\implies C.S.A=\cancel{\dfrac{924}{7}}\\ \\ \sf\twoheadrightarrow C.S.A=132cm{}^{2}$

$\sf{\blue{Cost\:of\: plastering=Rate\times C.S.A }}$

• Rate = ₹52 Per sq.m

$\sf\twoheadrightarrow Cost\:of\: plastering=52\times 132\\ \\ \sf\twoheadrightarrow Cost\:of\: plastering= 6864Rs$

$\underline{\boxed{\sf{Cost\:of\: plastering=6864 Rs}}}$

Answer 2

$</p><p>\huge{\tt{\pink{Hello!!! }}}$

$</p><p>\tt{\blue{Given \:- }}$

$</p><p>\tt{\purple{Inner \: Radius\: = \: 2.1m. }}$

$</p><p>\tt{\red{Depth \: = \: 10 m. }}$

$</p><p>\tt{\green{Inner \: Surface \: Area \: - }}$

$</p><p>\tt{\huge{\boxed{\boxed{\pink{C.SA \: = \: 2πrh \: = 132 m }}}}}$

$</p><p>\tt{\blue{Cost \: = \: Rs \: 6864. }}$