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    Question

    What approximate value will come in place of the question

    mark (?) in the following question? (Note: You are not expected to calculate the exact value.) (31.4)² - (18.2)² = ?
    A 550 Correct Answer Incorrect Answer
    B 650 Correct Answer Incorrect Answer
    C 612 Correct Answer Incorrect Answer
    D 769 Correct Answer Incorrect Answer
    E None of these Correct Answer Incorrect Answer

    Solution

    ATQ,

    Use identity: a² - b² = (a + b)(a - b)

    (31.4 + 18.2) = 49.6 ≈ 50

    (31.4 - 18.2) = 13.2 ≈ 13

    ⇒ 50 × 13 = 650

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