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JEE Advanced 2020Paper 2
Exam
JEE Advanced
Year
2020
Paper
Paper 2
Subject
Mathematics
Chapter
Probability

JEE Advanced 2020 · Paper 2 · Mathematics · Probability

Two fair dice, each with faces numbered 1, 2, 3, 4, 5 and 6 , are...

Two fair dice, each with faces numbered 1,2,3,4,51, 2, 3, 4, 5 and 66, are rolled together and the sum of the numbers on the faces is observed. This process is repeated till the sum is either a prime number or a perfect square. Suppose the sum turns out to be a perfect square before it turns out to be a prime number. If pp is the probability that this perfect square is an odd number, then the value of 14p14p is_____

Correct answer

0

Step-by-step solution

Perfect Square can be 44 or 99, which can be obtained by \left(1, 3\right), \left(3, 1\right), \left(2, 2\right), \left(6, 3\right)\left(3, 6\right), \left(5, 4\right), \left(4, 5\right).</p><p>PrimeNumbercanbe.</p><p>Prime Number can be2oror3oror5oror7oror11,whichcanbeobtainedby</p><p>(1,1),(1,2),(2,1),(1,4),(4,1),(2,3),(3,2),(1,6),(6,1),(5,2),(2,5),(3,4),(4,3),(6,5),(5,6), which can be obtained by </p><p>\left(1, 1\right), \left(1, 2\right), \left(2, 1\right), \left(1, 4\right), \left(4, 1\right), \left(2, 3\right), \left(3, 2\right), \left(1, 6\right), \left(6, 1\right), \left(5, 2\right), \left(2, 5\right), \left(3, 4\right), \left(4, 3\right), \left(6, 5\right), \left(5, 6\right)

PP(square or prime)=2236= \dfrac{22}{36}

P(Perfect square is oddperfect square before prime)=436+1436.436+1436.1436.436+....736+1436.736+1436.1436.736+......P\left(\dfrac{\text{Perfect square is odd}}{\text{perfect square before prime}}\right) = \dfrac{\dfrac{4}{36} + \dfrac{14}{36} . \dfrac{4}{36} + \dfrac{14}{36} . \dfrac{14}{36} . \dfrac{4}{36} + . . . .}{\dfrac{7}{36} + \dfrac{14}{36} . \dfrac{7}{36} + \dfrac{14}{36} . \dfrac{14}{36} . \dfrac{7}{36} + . . . . . .}

=(4361−1436)(7361−1436)=47=P= \dfrac{\left(\dfrac{\dfrac{4}{36}}{1 - \dfrac{14}{36}}\right)}{\left(\dfrac{\dfrac{7}{36}}{1 - \dfrac{14}{36}}\right)} = \dfrac{4}{7} = P

⇒14P=8⇒ 14P = 8

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