Given log 10(2) = 0.3010 and log 10(7) = 0.8451, compute log 10(2.8). Show the decomposition and calculation steps clearly.

Aptitude Logarithm Difficulty: Easy
Choose an option
  • A
    0.4471
  • B
    1.4471
  • C
    2.4471
  • D
    14.471
  • E
    None of these

Answer

Correct Answer: 0.4471

Explanation

Introduction / Context:We evaluate a common logarithm by breaking 2.8 into factors whose logs are known and using standard log identities.

Given Data / Assumptions:

  • log 10(2) = 0.3010
  • log 10(7) = 0.8451
  • We want log 10(2.8).

Concept / Approach:Write 2.8 = 28/10 = (4×7)/10, then apply log(A/B) = log A − log B and log(AB) = log A + log B.

Step-by-Step Solution:

log(2.8) = log(28) − log(10)log(28) = log(4×7) = log 4 + log 7 = 2·log 2 + log 7Compute: 2·0.3010 + 0.8451 = 0.6020 + 0.8451 = 1.4471Subtract log 10 = 1: 1.4471 − 1 = 0.4471

Verification / Alternative check:2.8 ≈ 10^0.4471 (since 10^0.4471 ≈ 2.8), confirming consistency with the computed value.

Why Other Options Are Wrong:1.4471 is log 28; 2.4471 or 14.471 are orders of magnitude too large; 0.4471 is the only value matching log 2.8.

Common Pitfalls:Forgetting to subtract 1 when converting from log 28 to log 2.8 (since 2.8 = 28/10) yields the common mistake 1.4471 instead of 0.4471.

Final Answer:0.4471

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