SURFACE AREAS

AND VOLUMES

• Sums based on Cuboid

Q. The dimensions of a cuboid in cm are 16 × 14 × 20.

Find its total surface area.

∴ Total surface area of the cuboid is 1648 cm².

Sol.

= 2

(16 × 14

+ 14 × 20

+ 16 × 20)

= 2

(224

+ 280

+ 320)

= 2

(824)

= 1648 cm²

What is formula for finding total surface area of cuboid ?

2(lb+bh+lh)

For given cuboid,

length (l ) = 16 cm

breadth (b) = 14 cm

height (h) = 20 cm

Total surface area of cuboid

= 2(lb + bh + lh)

= l × b × h

Q. The cuboid water tank has length 2 m, breadth 1.6 m and height 1.8 m.

Find the capacity of the tank in litres.

∴ Volume of cuboid water tank is 5760 litres.

Volume of cuboid water tank

Sol.

= 2

× 1.6

× 1.8

= 5.76 m³

= 5.76

× 1000 litres

= 5760 litres

[1m³ = 1000 litres]

Volume

What is formula for finding volume of cuboid ?

l × b × h

length (l ) = 2 m

breadth (b) = 1.6 m

height (h) = 1.8 m

We know that,

1 m³ = 1000 litres