Logarithm


  1. If log 90 = 1.9542 then log 3 equals to ?









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    Given log90 = 1.9542
    ⇒ log(32 x 10) = 1.9542
    ⇒ 2log 3 + log 10 = 1.9542

    Correct Option: C

    Given log90 = 1.9542
    ⇒ log(32 x 10) = 1.9542
    ⇒ 2log 3 + log 10 = 1.9542
    ∴ log 3 = 0.9542 / 2 = 0.4771


  1. If 2log4x = 1 + log4 (x-1), find the value of x. ?









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    ∵ 2log4x = 1 + log4(x-1)
    ⇒ log4x2 = log44 + log4(x-1)
    ⇒ x2 = 4(x-1)

    Correct Option: A

    ∵ 2log4x = 1 + log4(x-1)
    ⇒ log4x2 = log44 + log4(x-1)
    ⇒ x2 = 4(x-1)
    ⇒ x2 - 4x + 4 = 0
    ⇒ (x-2)2 = 0
    ∴ x = 2



  1. If log 3 = 0.477 and (1000)x = 3, then x equals to ?









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    ∵ (1000)x = 3
    ⇒ xlog 103 = log 3

    Correct Option: A

    ∵ (1000)x = 3
    ⇒ xlog 103 = log 3
    ⇒ 3x = log 3
    ∴ x = log 3 / 3 = 0.477 / 3 = 0.159


  1. If 55-x = 2x-5, find the value of x . ?









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    ∵ 55-x = 2x-5
    ⇒ 55-x = 2-(5-x)
    ⇒ (5-x)log 5 = -(5-x)log 2
    ⇒ (5-x)log 5 + (5-x)log 2 = 0

    Correct Option: A

    ∵ 55-x = 2x-5
    ⇒ 55-x = 2-(5-x)
    ⇒ (5-x)log 5 = -(5-x)log 2
    ⇒ (5-x)log 5 + (5-x)log 2 = 0
    ⇒ (5-x){log 5 + log 2 } = 0
    ⇒ (5-x){log10/2 + log 2 } = 0
    ⇒ (5-x){log10 - log 2 + log 2} = 0
    ⇒ 5-x = 0
    ∴ x = 5



  1. If log8 x + log4 x + log2x =11, then the value of x is ?









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    ∵ log23 x1 +log22 x1 + log2x = 11
    ⇒ 1/3log2x + 1/2log2x + log2x = 11

    Correct Option: D

    ∵ log23 x1 +log22 x1 + log2x = 11
    ⇒ 1/3log2x + 1/2log2x + log2x = 11
    ⇒ (1/3 + 1/2 +1)log2x = 11
    ⇒ 11/6log2x = 11
    ⇒ log2x = 11 x 6 / 11 =6
    ∴ x = 26 = 64