Which of the following is equivalent to log(125) 25?

It is important to note that both 125 and 25 are powers of 5. 5 to the third yields 125, 5 squared yields 25.
By definition of the logarithm, the number we are looking for is the number x for which holds. Using the above facts, we get:
.
Since the bases of the exponents are equal, we can equate the exponents. 3x=2. Hence, x=2/3. This the answer.