Answer - B
Explanation
Let the edge of the cube be X.
√(3 )X=12√(6)
⇒ X=12√(2)
Surface area = 6X2 = (6 x 12√(2) x12√(2)) m2 ≡ 1728 m2.
Answer - A
Explanation
Let the edge of the cube be X. Then,
6X2 = 1728
⇒ X2 = 288
⇒ X = 12√2 cm.
Volume = X3 = (12√2)3 cm3
= 3456√2 cm3.
Answer - A
Explanation
Volume of the wall = (1800 x 600 x 90) cm3.
Volume of 1 brick = (36 x 18 x 12) cm3.
Number of bricks=((1800 x 600 x 90)/( 36 x 18 x 12)=12500
Answer - B
Explanation
We have R = 6 cm and H = 8 cm.
Volume = (1/3)πR2H= (1/3)πx62x8=96π cm3
Q 5 - A room is 30 m long and 24 m broad. If the sum of the areas of the floor and the ceiling is equal to the sum of the areas of four walls, the volume of the hall is:
A - 96 m3
B - 960 m3
C - 9600 m3
D - 96000 m3
Answer - C
Explanation
Let the height be H
2(30 + 24) x H = 2(30 x 24)
⇒ H=(2(30 x 24))/(2(30 + 24))=(30 x 24)/54=40/3 m
⇒ Volume = 30 x 24 x 40/3 = 9600 m3
Answer - A
Explanation
External radius = 8 cm,
Internal radius = 6 cm.
Volume of steel = ( π x (82-62) x42) =1176 π cm3
Weight of steel = (1176 π x 12) gm = 51744 gm = 51.744 kg.
Answer - D
Explanation
L = 20 m, H = 16 m.
So, R = √(L2-H2) = √(202-162) = 12 m.
⇒ Curved surface area = πRL = (π x 12 x 20) m2 = 240π m2.
Answer - D
Explanation
Volume = πR2H= π x 72 x 60 = 9240 cm3
Curved surface area = 2πRH = (2 π x 7 x 60) cm2 =2640 cm2
Q 9 - If the volume of a cylindrical tank is 3696 m3 and the diameter of its base is 28 m, then find the depth of the tank.
A - 5 m
B - 6 m
C - 8 m
D - 14 m
Answer - B
Explanation
Let the depth of the tank be H meters. Then,
Volume = πR2H= π x 142 x H = 3696 m3
⇒ H=6 m
Answer - B
Explanation
Volume of 1 rod = (( 22/7) x (2/100) x (2/100) x 14 ) m3= 11/625 m3
Volume of steel = 1.76 m3
Number of rods = (1.76 x 625/11) = 100.
Answer - A
Explanation
Volume = (32 x 28 x 14) m3 = 12544 m3.
Surface area = [2 (32 x 28 + 28 x 14 + 32 x 14)] m2 = (2 x 1736) m2 = 3472 m2.
Answer - A
Explanation
Length of the longest pole=√(242+162+182)=34 m
Answer - B
Explanation
Distance covered in one revolution = ((44 X 2000)/1000) = 88m.
2πR = 88
2 x (22/7) x R = 88
⇒ R = 88 x (7/44) = 14 m.
Q 14 - A rectangular block 35 cm x 42 cm x 70 cm is cut up into an exact number of equal cubes. Find the least possible number of cubes.
A - 300
B - 200
C - 100
D - 50
Answer - A
Explanation
Volume of the block = (35 cm x 42 cm x 70 cm) cm3 = 300x73 cm3.
Side of the largest cube = H.C.F. of 35 cm , 42 cm and 70 cm = 7 cm.
Volume of this cube = (7 x 7 x 7) cm3 = 73 cm3.
Number of cubes = 300x73/73 = 300.
Answer - A
Explanation
Let their edges be X and Y. Then,
X3/Y3 = 8/125 (or) (X/Y)3 = (2/5)3 (or) (X/Y) = (2/5).
Ratio of their surface area = 6X2/6Y2 = X2/Y2 = (X/Y)2 = 4/25, i.e. 4:25.
Answer - B
Explanation
Volume = (4/3)πr3 =(4/3)*(22/7)*(21)*(21)*(21) cm3 = 38808 cm3.
Surface area = 4πr2 =(4*(22/7)*(21)*(21)) cm2 = 5544 cm2
Answer - A
Explanation
Let the breadth of the wall be X meters.
Then, Height = 10X meters and Length = 160X meters.
X x 10X x 160X = 25.6
⇒ X3=25.6/1600
=2/125
⇒X = ∛2/5 m
Q 18 - Two metallic right circular cones having their heights 4.1 cm and 4.3 cm and the radii of their bases 2.1 cm each have been melted together and recast into a sphere. Find the diameter of the sphere.
A - 2 cm
B - 3 cm
C - 4 cm
D - 5 cm
Answer - A
Explanation
Volume of sphere = Volume of 2 cones
= (1/3 π x (12) x 2.2 + 1/3 π x (1)2 x 1.8) = 4/3 π
Let the radius of sphere be R
4/3 π R3 = 4/3 π or R = 1cm
Hence , diameter of the sphere = 2 cm
Answer - B
Explanation
Curved surface area of roller = (2 π R H) = 2 x π x 1.4 x 3=132/5.
Area covered by the roller = 10 x (132/5) =264 m2
Q 20 - The curved surface area of a cylindrical pillar is 440 m2 and its volume is 1540 m3. Find the ratio of its diameter to its height.
A - 7:5
B - 6:5
C - 5:7
D - 6:7
Answer - A
Explanation
Curved surface area = (2 π R H) = 440
⇒ R x H=70 ... (1)
Volume = ⇒ R2H=1540
⇒ R2 x H =490 ... (2)
Solving 1 & 2 we get R=7 m H= 10 m
Required ratio = 2R/H =14/10 =7/5 =7:5
