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Question

Find the surface area of a sphere whose diameter is equal to 98 cm.

The correct answer is
$30,184$ cm$^2$

1. Identify the Question Type: This is a Mensuration problem involving the surface area of a sphere.

2. Step-by-Step Solution:

  • Find the radius: The diameter of the sphere is given as 98 cm. The radius (r) is half the diameter, so \(r = \frac{98}{2} = 49\) cm.
  • Formula for Surface Area: The formula for the surface area (A) of a sphere is \(A = 4\pi r^2\).
  • Substitute and Calculate: Substitute the value of the radius (r = 49 cm) into the formula:
  • \(A = 4 \times \pi \times (49)^2\)
  • \(A = 4 \times \pi \times 2401\)
  • Using \(\pi = \frac{22}{7}\), we get:
  • \(A = 4 \times \frac{22}{7} \times 2401\)
  • \(A = 4 \times 22 \times 343\)
  • \(A = 88 \times 343\)
  • \(A = 30184\) cm2

3. Core Logic/Pattern: The core logic is applying the correct formula for the surface area of a sphere and performing the calculation accurately.

4. Eliminate Incorrect Options: The incorrect options (29256, 39204, 33284) result from calculation errors or using an incorrect formula. They are not the result of the correct application of the surface area formula for a sphere.

5. Conclusion: The surface area of the sphere is 30,184 cm2.

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Important Questions from 3-D Mensuration

  1. A conical vessel has base radius 31 cm and height 45 cm. Water is poured into the vessel until it is $\frac{2}{3}$ full. Find the volume (in cm³) of water in the vessel.
  2. A solid metallic sphere of radius 10 cm is melted and recast into 125 identical spheres. What is the ratio of the surface area of the original sphere to the total surface area of 6 smaller spheres so formed?
  3. Find the volume (in cm³) of the largest right circular cone that can be cut out from a cube with an edge of 8 cm. Use $\pi = \frac{22}{7}$
  4. The volume of a solid cylinder is 5852 cm³ and its height is 38 cm. What is the total surface area of the solid cylinder? (Round your answer to the nearest integer) (Use $\pi = \frac{22}{7}$)
  5. Find the surface area of a sphere whose diameter is equal to 112 cm.
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