JAMB 2011 Mathematics · Question 11

If log318 + log33 - log3x = 3, Find x.

Options

  1. A.1
  2. B.2
  3. C.o
  4. D.3

Answer: B. 2

Explanation written with AI and checked against the answer key

Analyze the question: We have log₃18 + log₃3 − log₃x = 3 and need to find x.

Concept: Log laws (same base):

  • log a + log b = log(ab)
  • log a − log b = log(a/b)
  • log_b(N) = k means N = b^k

Solution:

  1. Combine the logs: log₃(18 × 3 / x) = 3 log₃(54/x) = 3
  1. Convert to index form: 54/x = 3³ = 27
  1. Solve for x: x = 54/27 = 2

Check: log₃18 + log₃3 − log₃2 = log₃(54/2) = log₃27 = 3 ✓

Answer: x = 2, which is option B.

Tip: When you see several logs with the same base, first combine them into a single log (add → multiply, subtract → divide), then switch to index form. Also remember that 3³ = 27, which is a common value in JAMB questions.

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