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61
The area of the largest triangle that can be inscribed in a semi-circle of radius r, is :
Discuss
Answer & Solution
Answer: Option A
Solution:
Required area :
$$\eqalign{ & = \frac{1}{2} \times {\text{Base}} \times {\text{Height}} \cr & = \left( {\frac{1}{2} \times 2r \times r} \right) \cr & = {r^2} \cr} $$
Area mcq solution image
62
If radius of a circle is 3 cm, what is the area of the circle in sq. cm ?
Discuss
Answer & Solution
Answer: Option B
Solution:
Given: Radius of a circle = 3 cm
Area of circle :
$$\eqalign{ & = \pi {r^2} \cr & = \pi \times {3^2} \cr & = 9\pi {\text{ sq}}{\text{.}}\,{\text{cm}} \cr} $$
63
The base of an isosceles is 14 cm and its perimeter is 36 cm. Find its area.
Discuss
Answer & Solution
Answer: Option A
Solution:
Let each equal side of isosceles triangle be x cm
Perimeter of an isosceles triangle = 36 cm
$$\eqalign{ & \therefore x + x + 14 = 36 \cr & \Rightarrow 2x = 36 - 14 \cr & \Rightarrow x = \frac{{22}}{2} \cr & \Rightarrow x = 11\,cm \cr} $$
Area mcq solution image
BD = DC = 7cm
From ΔABD
By using Pythagoras theorem :
$$\eqalign{ & AD = \sqrt {A{B^2} - B{D^2}} \cr & \,\,\,\,\,\,\,\,\,\,\,\, = \sqrt {{{11}^2} - {7^2}} \cr & \,\,\,\,\,\,\,\,\,\,\,\, = \sqrt {121 - 49} \cr & \,\,\,\,\,\,\,\,\,\,\,\, = \sqrt {72} \cr & \,\,\,\,\,\,\,\,\,\,\,\, = 3 \times 2\sqrt 2 \cr & \,\,\,\,\,\,\,\,\,\,\,\, = 6\sqrt 2 \,cm \cr} $$
∴ Area of ΔABC
$$\eqalign{ & = \frac{1}{2} \times BC \times AD \cr & = \frac{1}{2} \times 14 \times 6\sqrt 2 \cr & = 42\sqrt 2 {\text{ sq}}{\text{. cm}} \cr} $$
64
The total cost of flooring a room at Rs. 8.50 per square metre is Rs. 510. If the length of the room is 8 m, its breadth is :
Discuss
Answer & Solution
Answer: Option A
Solution:
Area of the floor :
$$\eqalign{ & = \left( {\frac{{510}}{{8.50}}} \right){m^2} \cr & = 60\,{m^2} \cr} $$
∴ Breadth of the room :
$$\eqalign{ & = \left( {\frac{{60}}{8}} \right)m \cr & = 7.5\,m \cr} $$
65
The diagonal of a rectangular field is 15 metres and the difference between its length its length and width is 3 metres. The area of the rectangular field is :
Discuss
Answer & Solution
Answer: Option D
Solution:
Let l and b be the length and breadth of the rectangle respectively.
Then,
$$\eqalign{ & \Rightarrow \sqrt {{l^2} + {b^2}} = 15 \cr & \Rightarrow \left( {{l^2} + {b^2}} \right) = {\left( {15} \right)^2} \cr & \Rightarrow {l^2} + {b^2} = 225 \cr} $$
And,
$$\eqalign{ & \Rightarrow l + b = 3 \cr & \Rightarrow {\left( {l - b} \right)^2} = 9 \cr & \Rightarrow {l^2} + {b^2} - 2lb = 9 \cr & \Rightarrow 225 - 2lb = 9 \cr & \Rightarrow 2lb = 216 \cr & \Rightarrow lb = 108 \cr} $$
Hence, area of the field $$ = lb = 108\,{m^2}$$
66
A room 5m × 8 m is to be carpeted leaving a margin of 10 cm from each wall. If the cost of the carpet is Rs. 18 per sq. meter, the cost of carpeting the room will be :
Discuss
Answer & Solution
Answer: Option A
Solution:
Area of the carpet :
= [(5 - 0.20) × (8 - 0.20)] m2
= (4.8 × 7.8) m2
= 37.44 m2
∴ Cost of carpeting :
= Rs. (37.44 × 18)
= Rs. 673.92
67
The length of a rectangular plot is thrice its breadth. If the area of the rectangular plot is 7803 sq. mtr, what is the breadth of the rectangular plot ?
Discuss
Answer & Solution
Answer: Option A
Solution:
Let the breadth of the plot be x metres
Then, length of the plot = (3x) metres
x × 3x = 7803
⇒ 3x2 = 7803
⇒ x2 = 2601
⇒ x = $$\sqrt {2601} $$
⇒ x = 51 m
68
A coaching institute wants to execute tiling work for one of its teaching halls 60 m long and 40 m wide with a square tile of 0.4 m side. If each tile costs Rs. 5, the total cost of tiles would be :
Discuss
Answer & Solution
Answer: Option D
Solution:
Number of tiles required :
$$\eqalign{ & = \frac{{{\text{Area of hall}}}}{{{\text{Area of each tile}}}} \cr & = \left( {\frac{{60 \times 40}}{{0.4 \times 0.4}}} \right) \cr & = 15000 \cr} $$
∴ Total cost of tiles :
= Rs. (15000 × 5)
= Rs. 75000
69
The ratio of the area of a square to that of the square drawn on diagonal is :
Discuss
Answer & Solution
Answer: Option C
Solution:
$$\eqalign{ & {\text{Required ratio}} \cr & = \frac{{{a^2}}}{{{{\left( {\sqrt 2 a} \right)}^2}}} \cr & = \frac{{{a^2}}}{{2{a^2}}} \cr & = \frac{1}{2} \cr & = 1:2 \cr} $$
70
The area of the four walls of a room is 120 m2 and the length is twice the breadth. If the height of the room is 4 m, then the area of the floor is :
Discuss
Answer & Solution
Answer: Option C
Solution:
Let the breadth = x metres and length = (2x) metres
Area of 4 walls = [2(2x + x)× 4] m2 = (24x) m2
∴ 24x = 120
⇒ x = 5
So, length = 10 m, and breadth = 5 m
Area of the floor = (10 × 5) m2 = 50 m2