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TS EAMCET · Maths · Probability

Two numbers \(b\) and \(c\) are chosen at random in succession without replacement from the set \(\{1,2,3, \ldots, 9\}\). Then the probability that \(\mathrm{x}^2+\mathrm{bx}+\mathrm{c}>0, \forall \mathrm{x} \in \mathbb{R}\) is

  1. A \(\frac{29}{72}\)
  2. B \(\frac{32}{81}\)
  3. C \(\frac{45}{143}\)
  4. D \(\frac{82}{125}\)
Verified Solution

Answer & Solution

Correct Answer

(A) \(\frac{29}{72}\)

Step-by-step Solution

Detailed explanation

\(x^2+b x+c>0, \forall x \in R\) \(\begin{aligned} \Rightarrow & D < 0 \\ & b^2-4 c < 0 \\ & b^2 < 4 c \end{aligned}\) Possible outcomes : \begin{array}{|c|c|c|} \hline \boldsymbol{b} & \boldsymbol{c} & Number of pairs \\ \hline 1 & 2,3,4,5,6,7,8,9 & 8 \\ \hline 2 &…