The decimal 5.09 converts to the mixed number 5 & 9/100
This is because the 9 is in the hundredths place.
If you need to convert to an improper fraction, then use the formula
a & b/c = (a*c + b)/c
So,
5 & 9/100 = (5*100+9)/100
5 & 9/100 = (500+9)/100
5 & 9/100 = 509/100