The decimal 0.5 is expressed as the fraction one-half. This is found by evaluating the decimal over 1, multiplying the fraction by 10 and then simplifying.
To change a decimal into a fraction, the decimal is placed over 1. Then, both the numerator and denominator are multiplied by a factor of 10 depending on how many digits are after the decimal point.
In the case of 0.5, there is one digit after the decimal, so it is only necessary to multiply by 10. When the numerator and denominator of the fraction 0.5/1 are multiplied by 10, it gives the fraction 5/10, which can be simplified. The number 5 goes into 10 twice. Dividing the numerator and denominator by 5 gives one-half.
The same result is given by reading 0.5 as 5/10, since the five is in the 10's place. This is written as 5/10, which simplifies to one-half.