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

Fraction	=	9/40
Make an equivalent fraction with denominator 1000: multiply numerator and denominator by 25. 9/40 = (9 x 25)/(40 x 25) = 225/1000.
As decimal	=	225/1000 = 0.225