If log10 2 = 0.3010, the value of log10 80 is:

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If log10 2 = 0.3010, the value of log10 80 is:

  1. A.

    1.6020

  2. B.

    1.9030

  3. C.

    3.9030

  4. D.

    None

Attempted by 2 students.

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Correct answer: B

Two logarithm laws apply here: the product rule log(a×b) = log a + log b, and the power rule log(an) = n·log a. Together they let the logarithm of a number be built up from the logarithms of its factors.

  1. Factor 80 as a power of 2 times 10: 80 = 23 × 10.

  2. Apply the product rule: log1080 = log10(23) + log1010.

  3. Apply the power rule to the first term: log10(23) = 3×log102.

  4. log1010 = 1, since 10 raised to the power 1 equals 10.

  5. Substitute log102 = 0.3010: 3×0.3010 = 0.9030.

  6. Add the two parts: 0.9030 + 1 = 1.9030.

Cross-check: log1080 must lie between log1010 = 1 and log10100 = 2, and closer to 2 since 80 is nearer 100 than 10 on a log scale — 1.9030 fits comfortably in that range.

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