21.

If the radius of a circle decreased by 50% its area is decreased by:

**Answer: Option 'A'**

**Original area = πr ^{2}
New area = π(r/2)^{2} = (πr^{2})/4
Reduction in area = [(πr^{2} - (πr^{2})/4]^{2} = (3πr^{2})/4
Reduction percent = ((3πr^{2})/4 × 1/(πr^{2} × 100) % = 75%**

22.

A rectangular room 14 m long, 12 m broad is surrounded by a varandah, 3 m wide. Find the area of the varandah?

**Answer: Option 'D'**

**Area of varandah = (l+b+2p)2p
= (14 + 12 + 6 ) 6
= 180 m**

23.

The area of the largest circle that can be drawn inside a square of side 28 Cm in length is:

**Answer: Option 'D'**

**Radius of required circle = 14 Cm
its area = 22/7 × 14 × 14
44 × 14 = 616 Cm**

24.

Area of four walls of a room is 99 m2. The length and breadth of the room are 7.5 m and 3.5m respectively. The height of the room is:

**Answer: Option 'C'**

**2(7.5+3.5)×h = 99
2(11)h = 99
22h = 99
h = 99/22 = 9/2 = 4.5 m**

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