Explanation:
a finite decimal number into a fraction is very easy.
remember what the different positions after the decimal point are worth :
tenths, hundredths, thousandths, tenthousandths, hundredthousandths, ...
0.225 covers thousandths.
how many ?
well, 225, of course.
so,
0.225 = 225/1000 = 9/40 × 25/25 = 9/40