RD Chapter 18- Surface Areas and Volume of a Cuboid and Cube Ex-18.1 |
RD Chapter 18- Surface Areas and Volume of a Cuboid and Cube Ex-VSAQS |

**Answer
1** :

Length of water tank (l) = 6 m

Breadth (b) = 5 m

and depth (h) = 4.5 m

∴ Volume of water in it = lbh

= 6 x 5 x 4.5 m3 = 135 m3

Capacity of water in litres = 135 x 1000 litres (1 m3 = 1000 l)

= 135000 litres

**Answer
2** :

Length of vessal (l) = 10 m

Breadth (b) = 8 m

Volume = 380 m3

**Answer
3** :

Length of pit (l) = 8m

Width (b) = 6 m

and depth (h) = 3 m

∴ Volume of earth digout = lbh

= 8 x 6 x 3 = 144 m3

Cost of digging the pit at the rate of ₹30 per m3

= 144 x 30 = ₹4320

**Answer
4** :

Let x, y, z be the three adjacent faces of the cuboid, then

x = 8 cm2, y = 18 cm2, z = 25 cm2

and let l, b, h are the dimensions of the cuboid, then

x = lb = 8 cm2

y = bh = 18 cm2

z = hl = 25 cm2

∴ Volume = lbh

**Answer
5** :
Let breadth of a room (b) = x

**Answer
6** :

Edge of first cube = 6 cm

Edge of second cube = 8 cm

and edge of third cube = 10 cm

∴ Volume of 3 cubes = (6)3 + (8)3 + (10)3 cm3

= 216 + 512 + 1000 cm3

= 1728 cm3

∴ Edge of so formed cube

**Answer
7** :

Volume of each volume = 512 cm3

∴ Side (edge) =

== 8 cm

Now by joining two cubes, then Length of so formed cuboid (l)

= 8 + 8 = 16 cm

Breadth (b) = 8 cm

and height (h) = 8 cm

∴ Surface area = 2(lb + bh + hl)

= 2[16 x 8 + 8 x 8 + 8 x 16] cm2

= 2[128 + 64 + 128] cm2

= 2 x 320 = 640 cm2

**Answer
8** :

Edge of metal cube = 12 cm

∴ Its volume = (Edge)3 = (12)3 cm33

= 1728 cm3

It is melted and form 3 cubes

Edge of one smaller cube = 6 cm

and edge of second smaller cube = 8 cm

∴ Volume of two smaller cubes = (6)3 + (8)3 cm3

= 216 + 512 cm3 = 728 cm3

∴ Volume of third smaller cube = 1728 – 728 = 1000 cm3

∴ Edge of the third cube =

= cm = 10 cm

**Answer
9** :

Length of cinema hall (l) = 100 m

Breadth (b) = 50 m

and height (h) = 18 m

∴ Volume of air in it = lbh

= 100 x 50 x 18 m3 = 90000 m3

Air required for one person = 150 m3

∴ Number of persons in the hall == 600 persons

**Answer
10** :

Weight of 1 cm3 = 0.25 kg

Breadth of the block (b) = 28 cm

Thickness (h) = 5 cm

and total weight of the block = 112 kg

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