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LOGARITHMS. 8
1
Example.
Log. % = log. 8 — log. 4
Log. 3 = 0.477121 = 10.477121 — 10
Log. 4 = 0.602060
Thus, log. % = 9.875061 — 10
This is also the logarithm of the decimal fraction 0.75.
RECIPROCALS.
Subtract the logarithm of the-number from log. 1, which is
10.000000 — 10, and the difference is the logarithm of the reci-
procal.
Example.
Find the reciprocal of 315.
Solution
:
Log. 1 = 10.000000 — 10
Log. 315 = 2.498311
Log. reciprocal of 315 = 7.501689 — 10
To this logarithm corresponds the decimal fraction
0.0031746, which is, therefore, the reciprocal of 315.
Simple Interest by Logarithms.
Add logarithm of principal, logarithm of rate of interest,
and logarithm of number of years ; from this sum subtract log-
arithm of 100. The difference is the logarithm of the interest.
Example.
Find the interest of $800 at 4% in 5 years.
Solution
:
Log. 800 = 2.90309
Log. 4, = 0.60206
0.69897
Log. 5 =
4.20412
Log. 100 = 2.00000
Log. interest = 2.20412 = $160 = Interest.
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