The number 0.45 written as a fraction is 45/100 or 9/20. Convert any decimal to a fraction by making the number behind the decimal point the numerator of the fraction and choosing the appropriate denominator: 1 followed by the same number of zeros as digits after the decimal.
Simplify the fraction by dividing both the numerator and denominator by the greatest common factor. If there are digits before the decimal, include them as whole numbers in front of the fraction so the answer becomes a mixed number. If the decimal number is negative, the new fraction or mixed number is also negative.