Rule: divide numerator by denominator, or make an equivalent fraction with denominator 10, 100, or 1000.

Fraction	=	9/20
Make an equivalent fraction with denominator 100: multiply numerator and denominator by 5. 9/20 = (9 x 5)/(20 x 5) = 45/100.
As decimal	=	45/100 = 0.45