Here is how you can write 0.125 as a fraction in an easy way:

= 0.125 

= 0.125 by 1

= 125 by 1000

= 25 by 200

= 5 by 40 

= 1/8 

Therefore, we can say that 0.125 can be written as 1/8 in the fractional expression in mathematics.

Basically, 0.125 is a decimal expression in mathematics. A fraction is a number that is denoted and written in the form of a denominator and numerator. Such as in the form of a by b (a being the numerator and b denominator).