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If log10 5 + log10 (5x + 1) = log10 (x + 5) + 1, then x is equal to:

/ Aptitude, Logarithm / By
Question:
If log10 5 + log10 (5x + 1) = log10 (x + 5) + 1, then x is equal to:

[A].

1

[B].

3

[C].

5

[D].

10

Answer: Option B

Explanation:

log10 5 + log10 (5x + 1) = log10 (x + 5) + 1

log10 5 + log10 (5x + 1) = log10 (x + 5) + log10 10

log10 [5 (5x + 1)] = log10 [10(x + 5)]

5(5x + 1) = 10(x + 5)

5x + 1 = 2x + 10

3x = 9

x = 3.