Free Topic-Wise General Studies MCQs
Conquer spatial reasoning with Dice, Cubes, and Painted Faces MCQs. Essential logical practice for the UPSC CSAT with detailed, professional explanations to visualize and solve complex problems.
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Explanation: Total unit cubes = 5³ = 125. Interior unpainted cubes = (5 − 2)³ = 27. Percentage = (27 / 125) × 100 = 21.6%.
Explanation: Using the formulas: cubes with exactly one painted face equal 6(n − 2)² = 6 × 36 = 216. Cubes with exactly two painted faces equal 12(n − 2) = 12 × 6 = 72. The ratio is 216 : 72 = 3 : 1.
Explanation: For an n×n×n cube cut into unit cubes, the cubes with exactly two painted faces lie along the edges but exclude the corners. There are 12 edges, and each edge contributes (n − 2) such cubes. Using the formula: 12(n − 2) = 12 × 3 = 36.
Explanation: The total number of unit cubes is 10³ = 1000. The cubes with no paint form an inner cube of side (10 − 2) = 8, giving 8³ = 512 unpainted cubes. Subtracting: 1000 − 512 = 488 cubes have paint on at least one face.
Explanation: A cube has 4 vertical edges. Each vertical edge contains (n − 2) cubes with exactly two painted faces (excluding the corner cubes which have three painted faces). Therefore: 4 × (5 − 2) = 4 × 3 = 12.
Explanation: Cubes with exactly three painted faces are always the 8 corner cubes of the original cube, regardless of the side length. Thus, there are always 8 such cubes.
Explanation: A 2 cm cube cut into 1 cm³ cubes yields 8 unit cubes, all of which are corner cubes. Since every unit cube occupies a corner position, each has three painted faces, leaving zero cubes with exactly one painted face.
Explanation: Cubes with at least two painted faces include the 8 corner cubes (three painted faces) and the non-corner edge cubes (two painted faces). Using the formulas: 8 + 4[(a − 2) + (b − 2) + (c − 2)] = 8 + 4 × 15 = 68.
Explanation: For a cuboid, cubes with exactly two painted faces lie on the edges excluding corners. The formula is: 4[(a − 2) + (b − 2) + (c − 2)]. Substituting: 4[(5 − 2) + (6 − 2) + (7 − 2)] = 4 × 12 = 48.
Explanation: Assume the bottom face is unpainted (the answer is the same for any single unpainted face due to symmetry). The cubes with exactly two painted faces are: (i) the four non-corner edges of the top face, giving 4(n − 2) = 8; (ii) the four non-corner vertical edges, giving 4(n − 2) = 8; and (iii) the four corners of the unpainted bottom face, giving 4. Total: 8 + 8 + 4 = 20.
Explanation: From the first position, 2 is adjacent to 3 and 5, so it cannot be opposite either of them. From the second position, 2 is adjacent to 4 and 6, so it cannot be opposite either of them. The only remaining face is 1, which must be opposite to 2.
Explanation: The total number of unit cubes is 6 × 8 × 10 = 480. The completely unpainted interior forms a cuboid of dimensions (6 − 2) × (8 − 2) × (10 − 2) = 4 × 6 × 8 = 192. Subtracting the unpainted from the total: 480 − 192 = 288.
Explanation: From Position I, 1 is adjacent to 2 and 3. From Position II, 1 is adjacent to 2 and 4. From Position III, 1 is adjacent to 3 and 5. Thus 1 cannot be opposite 2, 3, 4, or 5. The only remaining face is 6, which must be opposite to 1.
Explanation: For a cuboid, cubes with exactly one painted face lie at the center of each face. The formula is: 2[(a − 2)(b − 2) + (b − 2)(c − 2) + (c − 2)(a − 2)]. Substituting: 2[(2 × 3) + (3 × 4) + (4 × 2)] = 2 × 26 = 52.
Explanation: Using the principle of inclusion-exclusion for the three painted faces: each face has 4² = 16 painted cubes. The three pairs of adjacent painted faces share 3 edges with 4 cubes each. The common corner is counted three times and must be added back once. Thus: 3 × 16 − 3 × 4 + 1 = 48 − 12 + 1 = 37.
Explanation: For a cuboid, cubes with exactly two painted faces lie along the edges excluding corners. The formula is: 4[(a − 2) + (b − 2) + (c − 2)]. Substituting: 4[(3 − 2) + (4 − 2) + (5 − 2)] = 4 × 6 = 24.
Explanation: The top face has 4 edges. Each edge contains (n − 2) non-corner cubes with exactly two painted faces (painted on the top face and one adjacent side face), excluding the corner cubes which have three painted faces. Thus: 4 × (7 − 2) = 4 × 5 = 20.
Explanation: A cube has 4 vertical edges. Each vertical edge contains (n − 2) cubes with exactly two painted faces (painted on two adjacent vertical side faces), excluding the top and bottom corner cubes. Thus: 4 × (9 − 2) = 4 × 7 = 28.
Explanation: On a standard die, opposite faces sum to 7, so 4 is opposite 3. The four faces adjacent to 4 are therefore 1, 2, 5, and 6. Their sum is 1 + 2 + 5 + 6 = 14.
Explanation: The unpainted interior forms a cube of side (n − 2). For n = 3, this gives (3 − 2)³ = 1³ = 1 cube at the very center.
Explanation: Cubes with exactly one painted face lie at the center of each outer face, forming a square of side (n − 2). With 6 faces, the formula is: 6(n − 2)² = 6 × 16 = 96.
Explanation: Since 1, 2 and 3 are arranged clockwise around their common corner, if 2 is on top and 3 is on the front, then moving clockwise around that corner from above places 1 on the right face. This follows directly from the given clockwise order of the three numbers around the corner.
Explanation: Cubes with exactly three painted faces are always the 8 corner cubes. Cubes with exactly one painted face total 6(n − 2)² = 6 × 9 = 54. Adding these two groups: 8 + 54 = 62.
Explanation: When only two opposite faces are painted, every unit cube on those two faces has exactly one painted face because all adjacent faces are unpainted. Each painted face contains n² = 16 cubes, so the total is 2 × 16 = 32.
Explanation: The top face has 4 edges. Each edge contains (n − 2) cubes with exactly two painted faces (painted on the top face and one adjacent side face), excluding the corner cubes which have three painted faces. Thus: 4 × (8 − 2) = 4 × 6 = 24.
Explanation: From Position II, 5 is adjacent to 2 and 6, so it cannot be opposite either. From Position III, 5 is adjacent to 1 and 3, so it cannot be opposite either. The only remaining face is 4, which must be opposite to 5.
Explanation: There are 4 vertical side faces. On each face, the cubes with exactly one painted face form a square of side (n − 2) at the center. Therefore: 4 × (6 − 2)² = 4 × 16 = 64.
Explanation: From Position I, 1 is adjacent to 2 and 3, so it cannot be opposite either of them. From Position II, 1 is adjacent to 4 and 5, so it cannot be opposite either of them. The only remaining face is 6, which must be opposite to 1.
Explanation: There are 4 vertical side faces. On each face, the cubes with exactly one painted face form a square of side (n − 2) at the center, giving (5 − 2)² = 9 cubes per face. Therefore: 4 × 9 = 36.
Explanation: On a standard die with 1 opposite 6, 2 opposite 5, and 3 opposite 4, track the orientation through each roll. Starting with 1 on top: rolling south brings the front face (2) to the top; rolling east brings the right face (3) to the top; rolling south again brings the front face (6) to the top. The final top face is 6.
Explanation: With 1 on top, the bottom is 6. With 2 on the right, the left is 5. The remaining faces 3 and 4 must occupy the front and back positions. The sum is 1 + 6 + 3 + 4 = 14.
Explanation: For an n×n×n cube, the cubes with exactly two painted faces lie along the 12 edges, with each edge contributing (n − 2) cubes. Thus: 12 × (3 − 2) = 12 × 1 = 12.
Explanation: A standard die has faces numbered 1 through 6. The sum is 1 + 2 + 3 + 4 + 5 + 6 = 21.
Explanation: By definition, cubes with exactly two painted faces lie strictly along the edges between the corners. There are 12 edges, and each edge contributes (n − 2) such cubes. Thus: 12 × (7 − 2) = 12 × 5 = 60.
Explanation: The top face has 4 edges and the bottom face has 4 edges. Each edge contains (n − 2) non-corner cubes with exactly two painted faces (one face being the top or bottom, and the other being an adjacent side face). Thus: 8 × (6 − 2) = 8 × 4 = 32.
Explanation: On a standard die, opposite faces always sum to 7. Since 4 is on the bottom, the top face must be its opposite, which is 3 (because 4 + 3 = 7). The position of the front face does not alter the opposite-face relationship.
Explanation: When two adjacent faces are painted, the n cubes along their common edge have two painted faces. On each painted face, the remaining n² − n cubes have exactly one painted face. Thus: 2 × (4² − 4) = 2 × 12 = 24.
Explanation: Cubes with exactly one painted face lie at the center of each face, forming a square of side (n − 2). With 6 faces, the formula is: 6(n − 2)² = 6 × 7² = 6 × 49 = 294.
Explanation: The total number of unit cubes is 6³ = 216. The cubes with exactly one painted face total 6(n − 2)² = 6 × 16 = 96. Removing these: 216 − 96 = 120 cubes remain.
Explanation: A 2 cm cube cut into 1 cm³ cubes yields only 8 unit cubes, all of which are corner cubes. Every corner cube has exactly three painted faces, so there are no cubes with exactly two painted faces.
Explanation: Only the corner cubes have three faces exposed. At each corner, the three exposed faces belong to three different pairs of opposite faces, so each corner cube shows one red, one green, and one blue face. Since a cube has 8 corners, there are 8 such cubes.
Explanation: For a cuboid, the unpainted interior cubes form a smaller cuboid of dimensions (a − 2) × (b − 2) × (c − 2). Substituting: (5 − 2) × (5 − 2) × (7 − 2) = 3 × 3 × 5 = 45.
Explanation: The bottom face has 4 edges. Each edge contains (n − 2) cubes with exactly two painted faces (painted on the bottom face and one adjacent side face), excluding the corner cubes. Therefore: 4 × (4 − 2) = 4 × 2 = 8.
Explanation: On a standard die with 1 opposite 6, 2 opposite 5, and 3 opposite 4, the faces adjacent to 3 are 1, 2, 5, and 6. Rolling east brings the right face to the top. Rolling north then brings the back face to the top. Tracking the orientation through both rolls: after the first roll the top becomes 2, and after the second roll the top becomes 6.
Explanation: With 6 on the top face, the bottom face is 1 (opposite faces sum to 7). With 3 on the front face, the back face is 4. The remaining faces 2 and 5 occupy the left and right positions. The sum of the bottom, left, and right faces is 1 + 2 + 5 = 8, regardless of which of 2 or 5 is on the left or right.
Explanation: For a cuboid of dimensions a × b × c, the unpainted interior cubes form a smaller cuboid of dimensions (a − 2) × (b − 2) × (c − 2). Substituting the values: (5 − 2) × (7 − 2) × (9 − 2) = 3 × 5 × 7 = 105.
Explanation: Cubes with exactly three painted faces are always the 8 corner cubes. Cubes with no paint form the inner core of dimensions (n − 2)³. Adding these: 8 + (7 − 2)³ = 8 + 125 = 133.
Explanation: The largest face measures 6 cm × 7 cm. The cubes with exactly one painted face on this face form a rectangle at its center of dimensions (6 − 2) × (7 − 2). Thus: 4 × 5 = 20.
Explanation: From Positions I and II, 1 is adjacent to 2, 3, 4, and 5, so 1 must be opposite 6. From Positions I and III, 2 is adjacent to 1, 3, 4, and 6, so 2 must be opposite 5. The remaining pair is 3 opposite 4. Therefore, with 3 on top, the bottom face shows 4.
Explanation: Cubes with at least two painted faces include the 8 corner cubes (three painted faces) and the cubes lying strictly along the edges (two painted faces). Using the formulas: 12(n − 2) + 8 = 12 × 2 + 8 = 32.
Explanation: For a cuboid, the unpainted interior cubes form a smaller cuboid of dimensions (a − 2) × (b − 2) × (c − 2). Substituting: (6 − 2) × (8 − 2) × (10 − 2) = 4 × 6 × 8 = 192.
Explanation: With 1 on top, the bottom is 6. With 2 on the front, the back is 5. The remaining faces 3 and 4 occupy the right and left positions. The product of the four lateral faces is 2 × 5 × 3 × 4 = 120.
Explanation: When the four vertical faces are painted, each painted face has n² = 25 unit cubes with paint. The two vertical edges on each painted face contain n = 5 cubes each that have two painted faces (shared with adjacent painted faces). Thus, on each face, the cubes with exactly one painted face number n² − 2n = 25 − 10 = 15. For four faces: 4 × 15 = 60.
Explanation: The cubes with exactly two painted faces that are not on the top or bottom edges must lie on the 4 vertical edges. Each vertical edge contributes (n − 2) such cubes. Thus: 4 × (10 − 2) = 4 × 8 = 32.
Explanation: From Position II, 4 is adjacent to 1 and 5, so it cannot be opposite either. From Position III, 4 is adjacent to 3 and 6, so it cannot be opposite either. The only remaining face is 2, which must be opposite to 4.
Explanation: On any single face of an n×n×n cube, the cubes with exactly one painted face form a central square of side (n − 2) at the center of that face. For the top face, this is a 4 × 4 square: (6 − 2)² = 4² = 16.
Explanation: In any cuboid, exactly three faces are exposed only at the 8 corner cubes, regardless of the specific dimensions. Therefore, there are always 8 such cubes.
Explanation: Using the formula for cubes with exactly one painted face: 6(n − 2)² = 150. Dividing by 6 gives (n − 2)² = 25. Taking the square root: n − 2 = 5, so n = 7.
Explanation: Using the formula for cubes with exactly two painted faces: 12(n − 2) = 60. Dividing by 12 gives n − 2 = 5, so n = 7.
Explanation: Since 4 is on the bottom, the top face is its opposite, which is 3. Since 5 is on the back, the front face is its opposite, which is 2. The sum is 3 + 2 = 5.