Aspire Faculty ID #3634 · Topic: NIMCET 2012 · Just now
NIMCET 2012

A determinant is chosen at random from the set of all determinants of matrices of order 2 with elements 0 and 1 only. The probability that the determinant chosen is non-zero is:

Solution

Total $2\times2$ matrices with entries $0$ or $1$: $2^4 = 16$ 
Determinant: $ad - bc$ 
Non-zero determinant occurs in two cases. 

Case 1: $ad = 1$ and $bc = 0$ 
$a = 1, d = 1$ $(b,c)$ can be $(0,0), (0,1), (1,0)$ 
→ 3 matrices 

Case 2: $bc = 1$ and $ad = 0$ 
$b = 1,c = 1$ $(a,d)$ can be $(0,0), (0,1), (1,0)$ 
→ 3 matrices 
Total non-zero determinants = $3 + 3 = 6$
$P(\text{non-zero determinants})=\dfrac{6}{16}=\dfrac{3}{8}$

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