**Quantitative Aptitude Logarithms Study Material**

Put simply and confusingly, logarithms are inverse operators to exponents (just as subtraction to addition or division to multiplication). As you’ll see, taking a logarithm of something tells you what exponent you need to raise a base to to get that number.

Logarithm is an equivalent form of expressing an exponential identity.

**Definition** ; The logarithm of any number to a given base is the index of the power to which the base must be raised in order to equal the given number.

If b be any number, and p and N two other numbers such that b^{p} = N, thenp is called the logarithm of A’ to the base b and is written as log_{b}N. Thus the exponential identity bP = N is equivalent to logarithmic identity log_{b}N = p.

Logarithms with base e are called natural logarithms or Napierean logarithms after Scottish mathematician John Napier. Logarithms with base 10 are common logarithms. Generally, when the base is taken as 10, the subscript for the base is not written. Hence log N means log_{10}Y. (Logarithm with base e is usually written as In.)