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91
A patient in a hospital is given soup daily in a cylindrical bowl of diameter 7 cm. If the bowl is filled with soup to a height of 4 cm, how much soup the hospital has to prepare daily to serve 250 patients ?
Discuss
Answer & Solution
Answer: Option D
Solution:
Diameter of bowl = 7 cm
∴ Radius of bowl = $$\frac{2}{7}$$ cm
Height = 4 cm
∴ Volume of cylindrical bowl :
$$\eqalign{ & = \pi {r^2}h \cr & = \frac{{22}}{7} \times \frac{7}{2} \times \frac{7}{2} \times 4 \cr & = 154\,cu.cm \cr} $$
Hence, volume of soup for 250 patients :
$$\eqalign{ & = 154 \times 250 \cr & = 38500{\text{ c}}{{\text{m}}^3} \cr & = 38.5{\text{L}} \cr} $$
92
The breadth of a room is twice its height and half its length. The volume of the room is 512 cu.m. The length of the room is :
Discuss
Answer & Solution
Answer: Option A
Solution:
Let the height of the room be x metres
Then, breadth = 2x metres and length = 4x metres
∴ Volume of the room :
= (4x × 2x × x) m3
= (8x3) m3
8x3 = 512
⇒ x3 = 64
⇒ x = 4
∴ Length of the room is :
= 4x
= (4 × 4)
= 16 m
93
A closed box made of wood of uniform thickness has length, breadth and height 12 cm, 10 cm and 8 cm respectively. If the thickness of the wood is 1 cm, the inner surface area is :
Discuss
Answer & Solution
Answer: Option B
Solution:
Internal length = (12 - 2) cm = 10 cm
Internal breadth = (10 - 2) cm = 8 cm
Internal height = (8 - 2) cm = 6 cm
Inner surface area :
= 2 [10 × 8 + 8 × 6 + 10 × 6] cm2
= (2 × 188) cm2
= 376 cm2
94
From a cube of side 8 m, a square hole of 3 m side is hollowed from end to end. What is the volume of the remaining solid ?
Discuss
Answer & Solution
Answer: Option A
Solution:
Volume of the remaining solid :
= Volume of the cube - Volume of the cuboid cut out from it
= [(8 × 8 × 8) - (3 × 3 × 8)] m3
= (512 - 72) m3
= 440 m3
95
The dimensions of a rectangular box are in the ratio 2 : 3 : 4 and the difference between the cost of covering it with sheet of paper at the rate of Rs. 8 and Rs. 9.50 per square metre is Rs. 1248. Find the dimensions of the box in metres.
Discuss
Answer & Solution
Answer: Option C
Solution:
Let the length, breadth and height of the box be 2x, 3x and 4x respectively
Then, surface area of the box :
= 2 [2x.3x + 3x.4x + 2x.4x]
= [2(6x2 + 12x2 + 8x2)]
= 52x2
$$\eqalign{ & \therefore 52{x^2} = \frac{{1248}}{{1.50}} \cr & \Rightarrow 52{x^2} = 832 \cr & \Rightarrow {x^2} = \frac{{832}}{{52}} \cr & \Rightarrow {x^2} = 16 \cr & \Rightarrow x = 4 \cr} $$
Hence, the diameter of the box are 8 m, 12 m and 16 m

96
A cuboidal water tank contains 216 litres of water. Its depth is $$\frac{1}{3}$$ of its length and breadth is $$\frac{1}{2}$$ of $$\frac{1}{3}$$ of the difference between length and depth. The length of the tank is :
Discuss
Answer & Solution
Answer: Option C
Solution:
Let the length of the tank be x dm
Then, depth of the tank = $$\frac{x}{3}$$ dm
Breadth of the tank :
$$\eqalign{ & = \left[ {\frac{1}{2}{\text{ of }}\frac{1}{3}{\text{ of }}\left( {x - \frac{x}{3}} \right)} \right]{\text{dm}} \cr & = \left( {\frac{1}{2} \times \frac{1}{3} \times \frac{{2x}}{3}} \right){\text{dm}} \cr & = \frac{x}{9}\,{\text{dm}} \cr} $$
$$\eqalign{ & \therefore x \times \frac{x}{9} \times \frac{x}{3} = 216 \cr & \Rightarrow {x^3} = 216 \times 27 \cr & \Rightarrow x = 6 \times 3 \cr & \Rightarrow x = 18\,dm \cr} $$
97
A covered wooden box has the inner measures as 115 cm, 75 cm and 35 cm and the thickness of wood is 2.5 cm. Find the volume of the wood :
Discuss
Answer & Solution
Answer: Option C
Solution:
The external measures of the box are (115 + 5) cm, (75 + 5) cm, and (35 + 5) cm i.e., 120 cm, 80 cm and 40 cm
Volume of the wood :
= External volume - Internal volume
= [(120 × 80 × 40) - (115 × 75 × 35)] cm3
= (384000 - 301875) cm3
= 82125 cm3
98
Find the cost of a cylinder of radius 14 m and height 3.5 m when the cost of its metal is Rs. 50 per cubic meter :
Discuss
Answer & Solution
Answer: Option B
Solution:
Volume :
$$\eqalign{ & = \pi {r^2}h \cr & = \left( {\frac{{22}}{7} \times 14 \times 14 \times 3.5} \right){m^3} \cr & = 2156\,{m^3} \cr} $$
∴ Cost of the cylinder :
$$\eqalign{ & = {\text{Rs}}{\text{.}}\left( {2156 \times 50} \right) \cr & = {\text{Rs}}{\text{. 107800}} \cr} $$
99
The radii of the bases of two cylinders are in the ratio 3 : 4 and their height are in the ratio 4 : 3. The ratio of their volume is :
Discuss
Answer & Solution
Answer: Option C
Solution:
Let their radii be 3x, 4x and heights be 4y, 3y
Ratio of their volumes :
$$\eqalign{ & = \frac{{\pi \times {{\left( {3x} \right)}^2} \times 4y}}{{\pi \times {{\left( {4x} \right)}^2} \times 3y}} \cr & = \frac{{36}}{{48}} \cr & = \frac{3}{4}\,Or\,3:4 \cr} $$
100
Find the number of coins 1.5 cm in diameter and 0.2 cm thick, to be melted to form a right circular cylinder of height 10 cm and diameter 4.5 cm.
Discuss
Answer & Solution
Answer: Option C
Solution:
Volume one coin :
$$\eqalign{ & = \left( {\frac{{22}}{7} \times \frac{{75}}{{100}} \times \frac{{75}}{{100}} \times \frac{2}{{10}}} \right){\text{c}}{{\text{m}}^3} \cr & = \frac{{99}}{{280}}{\text{ c}}{{\text{m}}^3} \cr} $$
Volume of larger cylinder :
$$ = \left( {\frac{{22}}{7} \times \frac{9}{4} \times \frac{9}{4} \times 10} \right){\text{ c}}{{\text{m}}^3}$$
Number of coins :
$$\eqalign{ & = \left( {\frac{{22}}{7} \times \frac{9}{4} \times \frac{9}{4} \times 10 \times \frac{{280}}{{99}}} \right) \cr & = 450 \cr} $$