To add three logarithms with the same base:
log(a) + log(b) + log(c) = log(abc)
Example:
log10(2) + log10(3) + log10(5)
= log10(2 * 3 * 5)
= log10(30)
If the logarithms are already given as numbers:
1.3010 + 0.4771 + 0.6990
= 2.4771
Since:
log10(300) = 2.4771
the result corresponds to 300.
In general:
log(x) + log(y) + log(z) = log(x * y * z)
as long as all logs have the same base.