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logarithms

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1 Answer

Dear Yong,
 
If I understand the problem, what you are asking is what is x if
 
log(10) = log(30) - log(x) 
 
Whenever you see a "minus" sign in a logarithmic expression think "subtraction."  The given expression is mathematically identical to saying
 
10 = 30/x
 
x = 30/10 = 3
 
and that's the answer.  The beauty of this approach is that it is completely independent of the base of the logarithm.