Question

7. A well, 20 m deep, is 7 m in radius. Find the
cost of cementing the inner curved surface at
the rate of 15 per m2.​

Answer 1

Answer:

Find the volume, the lateral surface are and the total surface area of the cuboid whose dimensions are:

(i) length = 12 cm, breadth = 8 cm and height = 4.5 cm

(ii) length = 26 m, breadth = 14 m and height = 6.5 m

(iii) length = 15 m, breadth = 6 m and height = 5 dm

(iv) length = 24 m, breadth = 25 cm and height = 6 m

Answer 2

Given:-

• Height of the well = 20 m
• Radius of the well = 7 m

To find:-

• Cost of cementing it at a rate of ₹15 per m²

Formula to be used:-

$\longrightarrow$$\dashrightarrow$$\underline\pink{\boxed{\bf C.S.A = 2πrh }}$

Solution:-

:$\implies$ $\sf C.S.A = 2×\dfrac{22}{7}×7×20$

:$\implies$ $\sf C.S.A = 2×20×22$

:$\implies$ $\sf C.S.A = 880m²$

Now, Cost = C.S.A × Cost per m²

:$\implies$ $\sf Total Cost = 880×15$

:$\implies$ $\sf Total Cost = ₹ 13200$

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$\small\fbox{Additional\: information}$

• Total surface area of cylinder:-

$\dashrightarrow$$\underline\red{\boxed{\bf T.S.A = 2πr(r+h) }}$

• Volume of the Cylinder :-

$\dashrightarrow$$\underline\green{\boxed{\bf Volume = πr²h }}$

• T.S.A of Cone:-

$\dashrightarrow$$\underline\blue{\boxed{\bf T.S.A = πr(r+l) }}$

here, l ( slant height ) is calculated by:-

$\underline{\boxed{\sf l²=r²+h²}}$

• C.S.A of Cone:-

$\dashrightarrow$$\underline\orange{\boxed{\bf C.S.A = πrl }}$

• Volume of Cone:-

$\dashrightarrow$$\underline\purple{\boxed{\bf Volume = \dfrac{1}{3}×πr³ }}$