Surface and Area

Q 5: Find the surface area of a 8 cm x 7 cm x 3 cm brick. A)222 cm square B)202 cm square C)104 cm square D)None of these Answer : Option B Explanation: l=8 , b=7 , h=3 Surface area of a cuboid = 2(lb+bh+hl) cm square So, Surface area of a brick = 2(8 x 7 + 7 x 3 + 3 x 8) cm square = 202 cm square Q 6: The perimeter of one face of a cube is 24 cm. Its volume will be: A)216 cm cube B)118 cm cube C)224 cm cube D)180 cm cube Answer : Option A Explanation: Edge of cude = 24/4 = 6 cm Volume = a x a x a = 6 x 6 x 6 = 216 cm cube Q 7: If the volume of two cubes are in the ratio 8:1, the ratio of their edges is: A)3:1 B)2:8 C)4:1 D)2:1 Answer : Option D Explanation: Let the edges be a and b of two cubes, then a3/b3=8/1 (a/b)a3=(2/1)a3 a/b=2/1 a:b=2:1 Q 8: There are bricks with 20 cm x 10 cm x 9 cm dimensions. Find the total number of bricks required to construct a wall 14 m long, 4 m high and 60 m thick with 10% of wall filled with mortar. A)16800 B)9800 C)14500 D)None of these Answer : Option A Explanation: So as per question, Volume of wall=(1400 x 400 x 60)cm3 Volume of bricks= 90% of volume of wall [(90/100) x 1400 x 400 x 60]cm3 Volume of 1 brick = (20 x 10 x 9)cm3 Number of Bricks required [(90/100) x (1400 x 400 x 60)]/(20 x 10 x 9)=16800

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