JAMB 1985 · UME · Q8

Logarithms

Without using tables, evaluate $\log_2 4 + \log_4 2 - \log_{25} 5$ .

Worked solution (try it first)

$2^2 = 4$ , so $\log_2 4 = 2$ .
$4^{\frac12} = 2$ , so $\log_4 2 = \frac12$ .
In the same way $25^{\frac12} = 5$ , so $\log_{25} 5 = \frac12$ .
So the value is $2 + \frac12 - \frac12 = 2$ , option E.

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