To make a decimal into a fraction, we look at the place value. One place to the right of the decimal is the tenths place, and can be represented with a denominator of 10 and a numerator of the number given. So our first digit, 4, can be written as 4/10.
Repeat this of making 0.4 into 4/10 with each place going to the right, adding one zero for each place. 5 is the digit, and that's the hundredths place with two zeroes in the denominator. That can be written as 5/100.
To get a final fraction, add all the fractions you made together.
4/10 + 5/100
= 40/100 + 5/100 Getting common denominators
= 45/100
= 9/20 Simplifying by dividing top and bottom by 5
Thus 0.45, as a fraction, is
.