Q.

If p and q are chosen randomly from the set {1, 2, 3, 4, 5, 6, 7, 8, 9, 10} with replacement, then the probability that the roots of the equation x2 + px + q = 0

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a

are real is 33/50

b

are imaginary is 19/50

c

are real and equal is 3/50

d

are real and distinct is 3/5

answer is B.

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Detailed Solution

Roots of x2 + px + q = 0 will be real if p2≥4q.The possible selections are as follows:Therefore, number of favourable ways is 62 and total number of ways is 102 = 100. Hence, the required probability is62/100 = 31/50.The probability that the roots are imaginary is1 - 31/50 = 19/50.Roots are equal when (p, q) ≡ (2, 1), (4, 4), (6,9). The probability that the roots are real and equal is 3/50. Hence, probability that the roots are real and distinct is 3/5.
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If p and q are chosen randomly from the set {1, 2, 3, 4, 5, 6, 7, 8, 9, 10} with replacement, then the probability that the roots of the equation x2 + px + q = 0