JEE MainMathematicsPermutations and CombinationsMCQ+4 / −1
The number of square matrices of order 5 with entries from the set {0, 1}, such that the sum of all the elements in each row is 1 and the sum of all the elements in each column is also 1, is :
- A125
- B150
- C225
- D120
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Correct answer: D
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Let the matrix be a matrix with entries from .
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Given conditions:
- Sum of elements in each row is .
- Sum of elements in each column is also .
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Since entries are only or , the condition “sum of each row is 1” means:
- In each row, there is exactly one entry equal to and the remaining entries are .
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Similarly, “sum of each column is 1” means:
- In each column, there is exactly one entry equal to and the remaining entries are .
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Therefore, such a matrix is exactly a permutation matrix of order .
- A permutation matrix is obtained by placing exactly one in each row and each column.
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Count such matrices:
- In the first row, the can be placed in any of columns.
- In the second row, it must be in one of the remaining columns.
- In the third row, one of the remaining columns.
- In the fourth row, one of the remaining columns.
- In the fifth row, the last remaining column.
Hence total number is
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Checking options:
- A: ❌
- B: ❌
- C: ❌
- D: ✅
Therefore, the required number of matrices is
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