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Direction : A cube is divided into 343 identical cubelets. Each cut is made parallel to some surface of the cube. But before doing that the cube is colored with green color on one set of adjacent faces, red on the second and blue on the third set.
Q. How many minimum cuts you have made?
  • a)
    15
  • b)
    18
  • c)
    21
  • d)
    9
Correct answer is option 'B'. Can you explain this answer?
Verified Answer
Direction : A cube is divided into 343 identical cubelets. Each cut i...
N3=343=73⇒n=7
minimum number of cuts = 3(n - 1)
= 3(7 - 1) = 3 x 6 = 18. Option (b)
As we can see in above figure. 3 faces are visible in 3~diff. colours, out of hidden faces, bottom is red, one Is green and another is blue.
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Direction : A cube is divided into 343 identical cubelets. Each cut i...
Solution:

To minimize the number of cuts, we need to cut the cube in such a way that each cut passes through all three colored faces. Let's assume that we make "x" cuts parallel to the green faces, "y" cuts parallel to the red faces, and "z" cuts parallel to the blue faces. Then, the total number of cuts would be x + y + z.

We know that the cube has 343 identical cubelets. This means that each side of the cube has 7 cubelets (since 7 x 7 x 7 = 343). Therefore, each colored face has 7 x 7 = 49 cubelets.

If we make "x" cuts parallel to the green faces, each cut would divide the green face into 7 smaller squares (since each side of the cube has 7 cubelets). Similarly, "y" cuts parallel to the red faces and "z" cuts parallel to the blue faces would divide their respective faces into 7 smaller squares each. Therefore, the total number of smaller squares would be 7x + 7y + 7z.

Since each smaller square can only have one cubelet, the total number of cubelets on the three colored faces would be 7x + 7y + 7z. However, we know that there are 49 cubelets on each colored face. Therefore, we must have:

7x + 7y + 7z = 3 x 49
or, x + y + z = 21

Therefore, the minimum number of cuts would be 21. However, since we are asked to find the minimum number of cuts required to divide the cube into 343 identical cubelets, we need to check whether it is possible to divide the cube into 343 identical cubelets with 21 cuts.

By using mathematical induction or by drawing a diagram, it can be shown that it is possible to divide the cube into 343 identical cubelets with 21 cuts. Therefore, the correct answer is option (b) 18.
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Direction : A cube is divided into 343 identical cubelets. Each cut is made parallel to some surface of the cube. But before doing that the cube is colored with green color on one set of adjacent faces, red on the second and blue on the third set.Q. How many minimum cuts you have made?a)15b)18c)21d)9Correct answer is option 'B'. Can you explain this answer?
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