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Mathematics

The probability of answering a question correctly is 25\dfrac{2}{5} and probability of not answering the same question correctly is x15\dfrac{x}{15}. The value of x is :

  1. 6

  2. 9

  3. 15

  4. 5

Probability

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Answer

Since, answering the question correctly or not are complementary events.

∴ Probability of answering the question correctly + Probability of answering the question incorrectly = 1

⇒ 25+x15\dfrac{2}{5} + \dfrac{x}{15} = 1

⇒ 6+x15\dfrac{6 + x}{15} = 1

⇒ x + 6 = 15

⇒ x = 15 - 6 = 9.

Hence, Option 2 is the correct option.

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