I'll give you an example.
0.045
there are 3 numbers after the decimal point so there will be a 1 followed by 3 zeros on the bottom. That is 1000
45 goes on the top. so we have $$\frac{45}{1000}$$ This can be simplified by dividing both the top and the bottom by 5 so
$$\frac{45}{1000}=\frac{9}{200}$$
Does that help?
I'll give you an example.
0.045
there are 3 numbers after the decimal point so there will be a 1 followed by 3 zeros on the bottom. That is 1000
45 goes on the top. so we have $$\frac{45}{1000}$$ This can be simplified by dividing both the top and the bottom by 5 so
$$\frac{45}{1000}=\frac{9}{200}$$
Does that help?