Mensuration
- If each edge of a cube is increased by 50%, the percentage increase in its surface area is
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Percentage increase = 50 + 50 + 50 × 50 % = 125 % 100 Correct Option: D
Percentage increase = 50 + 50 + 50 × 50 % = 125 % 100
- Three solid iron cubes of edges 4 cm, 5 cm and 6 cm are melted together to make a new cube. 62 cm² of the melted material is lost due to improper handling. The area (in cm²) of the whole surface of the newly formed cube is
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Volume of all three cubes = (4² + 5² + 6²) cu.cm.
= (64 + 125 + 216) cu.cm. = 405 cu.cm.
∴ Volume of new cube = 405 – 62 = 343 cu.cm.
∴ Edge of cube = ³√343 = 7 cm.
∴ Surface area = 6 × 7² = 294 sq. cm.Correct Option: A
Volume of all three cubes = (4² + 5² + 6²) cu.cm.
= (64 + 125 + 216) cu.cm. = 405 cu.cm.
∴ Volume of new cube = 405 – 62 = 343 cu.cm.
∴ Edge of cube = ³√343 = 7 cm.
∴ Surface area = 6 × 7² = 294 sq. cm.
- A square of side 3 cm is cut off from each corner of a rectangular sheet of length 24 cm and breadth 18 cm and the remaining sheet is folded to form an open rectangular box. The surface area of the box is
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Length of box = 24 –( 2 × 3) = 18 cm
Width of box = 18 – 2 × 3 = 12 cm
Height of box = 3 cm
∴ Surface area of box = 18 × 12 + 2 (12 × 3 + 3 × 18)
= 216 + 180 = 396 sq. cmCorrect Option: B
Length of box = 24 –( 2 × 3) = 18 cm
Width of box = 18 – 2 × 3 = 12 cm
Height of box = 3 cm
∴ Surface area of box = 18 × 12 + 2 (12 × 3 + 3 × 18)
= 216 + 180 = 396 sq. cm
- A solid right circular cylinder and a solid hemisphere stand on equal bases and have the same height. The ratio of their whole surface area is:
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Radius of cylinder = r units and height = r units
[∵ height of hemisphere = radius]
∴ Required ratio = 2πr² + 2πr² : 2πr² + πr²
= 4 : 3Correct Option: C
Radius of cylinder = r units and height = r units
[∵ height of hemisphere = radius]
∴ Required ratio = 2πr² + 2πr² : 2πr² + πr²
= 4 : 3
- The base of a cone and a cylinder have the same radius 6 cm. They have also the same height 8 cm. The ratio of the curved surface of the cylinder to that of the cone is
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Slant height of cone l = √6² + 8²
= √36 + 64 = √100 = 10 cm
∴ Curved surface of cylinder : Curved surface of cone = 2πrh : πrl
= 2h : l = 16 : 10 = 8 : 5Correct Option: A
Slant height of cone l = √6² + 8²
= √36 + 64 = √100 = 10 cm
∴ Curved surface of cylinder : Curved surface of cone = 2πrh : πrl
= 2h : l = 16 : 10 = 8 : 5