JAMB - Mathematics (1980 - No. 32)
Given log 2 = 0.69, log3 = 1, 10 and log7 = 1.90, all to a fixed base, find log 10.5 to the same base without using tables.
1.03
2.31
3.69
10.5
25
Explanation
log 10.5 = log \(\frac{21}{2}\)
= log 21 - log 2
= log(3 x 7) - log 2
= log 3 + log 7 - log 2
= 1.10 + 1.90 - 0.69
= 3 - 0.69
= 2.31
= log 21 - log 2
= log(3 x 7) - log 2
= log 3 + log 7 - log 2
= 1.10 + 1.90 - 0.69
= 3 - 0.69
= 2.31
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