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## Tamilnadu Samacheer Kalvi 9th Maths Solutions Chapter 7 Mensuration Ex 7.4

Multiple Choice Questions:

Question 1.

The semi-perimeter of a triangle having sides 15 cm, 20 cm and 25 cm is

(1) 60 cm

(2) 45 cm

(3) 30 cm

(4) 15 cm

Solution:

(3) 30 cm

Question 2.

If the sides of a triangle are 3 cm, 4 cm and 5 cm, then the area is

(1) 3 cm^{2}

(2) 6 cm^{2}

(3) 9 cm^{2}

(4) 12 cm^{2}

Solution:

(2) 6 cm^{2}

Question 3.

The perimeter of an equilateral triangle is 30 cm. The area is

(1) \(10 \sqrt{3}\) cm^{2}

(2) \(12 \sqrt{3}\) cm^{2}

(3) \(15 \sqrt{3}\) cm^{2}

(4) \(25 \sqrt{3}\) cm^{2}

Solution:

3a = 30

a = 10 cm

Solution:

(4) \(25 \sqrt{3}\) cm^{2}

Question 4.

The lateral surface area of a cube of side 12 cm is

(1) 144 cm^{2}

(2) 196 cm^{2}

(3) 576 cm^{2}

(4) 664 cm^{2}

Hint: 4a^{2} = 4 × 12 × 12 = 4 × 144 = 576 cm^{2}

Solution:

(3) 576 cm^{2}

Question 5.

If the lateral surface area of a cube is 600 cm^{2}, then the total surface area is

(1) 150 cm^{2}

(2) 400 cm^{2}

(3) 900 cm^{2}

(4) 1350 cm^{2}

Hint:

4a^{2} = 600 cm^{2}

Solution:

(3) 900 cm^{2}

Question 6.

The total surface area of a cuboid with dimension 10 cm × 6 cm × 5 cm is

(1) 280 cm^{2}

(2) 300 cm^{2}

(3) 360 cm^{2}

(4) 600 cm^{2}

Hint:

TSA = 2 (lb + bh + hl)

= 2 (10 × 6 + 6 × 5 + 5 × 10) = 2 (60 + 30 + 50) = 2 (140) = 280 cm^{2}

Solution:

(1) 280 cm^{2}

Question 7.

If the ratio of the sides of two cubes are 2 : 3, then ratio of their surface areas will be

(1) 4 : 6

(2) 4 : 9

(3) 6 : 9

(4) 16 : 36

Hint:

a : b = 2 : 3

4a^{2} : 4b^{2} = 4 × 2^{2} : 4 : 3^{2}

⇒ 16 : 36

⇒ 4 : 9

Solution:

(2) 4 : 9

Question 8.

The volume of a cuboid is 660 cm3 and the area of the base is 33 cm^{2}. Its height is

(1) 10 cm

(2) 12 cm

(3) 20 cm

(4) 22 cm

Hint:

V = 660 cm^{3}

lb = 33 cm^{2}

h = ?

lbh = 660

Solution:

(3) 20 cm

Question 9.

The capacity of a water tank of dimensions 10 m × 5 m × 1.5 m is

(1) 75 litres

(2) 750 litres

(3) 7500 litres

(4) 75000 litres

Hint: Volume of cuboid = l × b × h

Solution:

(4) 75000 litres

Question 10.

The number of bricks each measuring 50 cm × 30 cm × 20 cm that will be required to build a wall whose dimensions are 5m × 3m × 2m is

(1) 1000

(2) 2000

(3) 3000

(4) 5000

Hint:

Solution:

(1) 1000