- A
- B
- C
- D
View written solutionFree
Correct answer: C
Let the matrix be where each entry is chosen from the set of first primes:
Since each of the entries can be chosen independently in ways, the total number of matrices is
We need the probability that the matrix is singular.
1. Condition for singularity
A matrix is singular iff its determinant is zero: that is,
So we must count the number of ordered quadruples such that
2. Use prime factorization structure
All entries are prime numbers.
If then the product of the two primes on the left equals the product of the two primes on the right.
By unique factorization, the multiset of primes in must be the same as the multiset of primes in .
So the only possibilities are:
- and , or
- and .
Equivalently, once is chosen, must be either or .
3. Count singular matrices carefully
We count ordered pairs first.
There are choices for .
Case 1:
Number of such pairs:
For each such pair, can be chosen in exactly ways: So contribution is
Case 2:
Number of such pairs:
Then the two possibilities for coincide, since So for each such pair there is only valid choice: Thus contribution is
Hence total number of singular matrices is
4. Compute probability
Therefore,
5. Compare with options
corresponds to Option C.
Final Answer
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