# CBSE Class 10-Mathematics: Chapter – 13 Surface Areas and Volumes Part 20 (For CBSE, ICSE, IAS, NET, NRA 2022)

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**Question 17**:

The radius of the base and the height of solid right cylinder are in the ratio and its volume is . Find the total surface area of the cylinder.

**Answer**:

Let r be the radius of the base and h be the height of the solid right circular cylinder.

Volume of the cylinder

Surface area of cylinder

**Question 18**:

A toy is in form of a cone mounted on a hemisphere of common base radius 7 cm. The total height of the toy is , find the total surface area of the toy.

**Answer**:

Total surface area of . of hemisphere . of cone

Here,

T. S. A. of

**Question 19**:

A well in diameter and deep be dug in rectangular field by . The earth taken out is spread evenly on the field. Find the level of the earth raised in the field.

**Answer**:

Radius of well

Depth of well

Volume of earth taken out

Area of field excluding well

Level of earth raised

**Question 20**:

A solid sphere of radius is melted into a hollow cylinder of uniform thickness. If the external radius of the base of cylinder is and its height is , find the uniform thickness of the cylinder.

**Answer**:

Volume of sphere

Let the internal radius of cylinder

External radius

Volume

Volume of the hollow cylinder Volume of sphere