Page 250 - ICSE Math 8

MENTAL MATHS

1. Choose the correct option.

(a) The volume of a cube whose edge is 3x is:
2
2
3
(i) 27x (ii) 18x (iii) 18x (iv) 27x 3
(b) The maximum length of a rod that can be kept in a cuboidal box of dimension 12 cm × 9 cm × 8 cm is:
(i) 17 cm (ii) 19 cm (iii) 18 cm (iv) 13 cm
(c) The lateral surface area of a cuboid of dimension 11 cm × 8 cm × 5 cm is:

2
3
3
(i) 19 cm (ii) 190 cm (iii) 366 cm (iv) 366 cm 2
(d) The sum of the areas of all six faces of a cuboid is the ___________ of the cuboid.
(i) volume (ii) surface area
(iii) lateral surface area (iv) diagonal
3
(e) The volume of an oil tank is 4 m . Its capacity in litres is:
(i) 40,000 (ii) 4,000 (iii) 400 (iv) 40
(f) The surface area of an open box whose length, breadth and height are l, b and h respectively is:

(i) 2(lb + bh) + hl (ii) 2(bh + hl) + lb (iii) 2(lb + bh + hl) (iv) 2(lb + hl) + bh
2. Write True or False.
(a) The six faces of a cube are squares of same size.

(b) If the length of an edge of a cubical mug is 10 cm, then the capacity of the mug will be 1 L.
(c) A hollow cylinder has a curved lateral surface with congruent circular ends.

(d) When the ratio of the volumes of two cubes is 8 : 27, the ratio of their surface areas will also be 8 : 27.
(e) The axis of a cylinder is always perpendicular to the circular ends.
3. Fill in the blanks.

(a) The occupied by a solid is called its _________________.
(b) 1 kL = _________________ m 3

(c) A solid bound by two _________________ cylinders of same height and different _________________
is called a hollow cylinder.

3
(d) 1 kL = _________________ dm = _________________ cm 3
(e) The volume of a cuboid of dimensions 8 m × 6 m × 3 m is _________________.

PRACTICE TIME

1. How many bricks will be required for a wall which is 4.9 m long, 8 m high and 2.4 m thick if each brick
measures 24 cm × 12.25 cm × 4 cm?

2. A swimming pool is 24 m long and 15 m broad. When few men dive into the pool, the height of the water
3
rises by 1 cm. If the average amount of water displaced by one man is 0.1 m , how many men are there
in the pool?

3. If the length, breadth and height of a cuboid are in the ratio 6 : 5 : 4 and its total surface area is
2
33,300 m , find the dimensions of the cuboid.

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