Question

What is the cost price of steel coating of a

cylindrical iron rod at the rate of Rs.3.5per

100cm2

?

(a) Rs.79.20

(b) Rs.89.20

(c) Rs.85.56

(d) Rs.71.28​

Answer 1

Answer:

Answer is(B)

89.20

Hope it's help you.

Answer 2

Solution :-

Let us assume that, height of each cylindrical rod is h cm.

so,

→ Volume of big iron ball = Volume of 4 cylindrical rods.

→ (4/3) * π * (R)³ = 4 * π * (r)² * h

4π will be cancel from both sides,

→ (36/2)³ = 3 * (12/2)² * h

→ 18 * 18 * 18 = 3 * 6 * 6 * h

→ 6 * 3 * 3 = h

→ h = 54 cm.

then,

→ CSA of a cylindrical rod = 2πrh = 2 * 3.14 * 6 * 54 = 2034.72 cm².

therefore,

→ 100cm² of area cost = Rs.3.5

→ 1 cm² of area cost = (3.5/100)

→ 2034.72 cm² of area cost = (3.5 * 2034.72) / 100 = Rs.71.21 (Ans.)

Hence, cost price of steel coating of a cylindrical iron rod is Rs.71.21 .

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