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JAMB Mathematics 1994 Question 20

Question 20

Logarithms

Find the value of r if log10r2 + log10r4 + log10r8 + log10r16 + log10r32 = 63

  1. A.10−1
  2. B.100
  3. C.10
  4. D.102
Show the answer and explanation

Answer: C (10)

Explanation

Adding logs multiplies the powers: the left side is (2 + 4 + 8 + 16 + 32) log r = 62 log r. So log r ≈ 1 and r ≈ 10 (exactly 10 if the sum also has a log10r term, making 63 log r = 63).