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Q.

A bucket is in the form of a frustum of a cone with a capacity of 12308.8 cm3 of water. The radii of the top and bottom circular ends are 20 cm and 12 cm respectively. Find the area of the metal sheet used in its making.

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a

2402.28 cm2

b

2352.28 cm2

c

2162.28 cm2

d

2094.28 cm2

answer is C.

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Detailed Solution

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Given,
Frustum of a cone volume = 12308.8 cm3
Upper radius r1 is 20 cm.
Lower radius r2 is 12 cm.
We know that,
Frustum of cone volume=13πhr12+r22+r1r2       (h=height)
12308.8=π3h(20×20+12×12+20×12)
12308.8×3=πh(400+144+240)
12308.8×3=227h(784)
h=12308.8×3×722×784
h = 14.99

h = 15 cm (approx)
So, the slant height (l) of the bucket can be given as,
l=h2+r1-r22
l=152+(20-12)2
l=225+(8)2
l=225+64
l=289
l=17 cm
Therefore, the surface area of the bucket can be given as,
=πr1+r2l+πr22
=π20+1217+π122
=π3217+π122
=π544+144 =2162.28 cm2
Therefore, the area of the metal sheet is 2162.28 cm2.
Hence, option 2162.28 cm2 is correct.

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