Well when you convert fractions to decimals, you simply divide the numerator by the dominator.
To convert decimals to percents, you take the fraction and divide the numerator by the dominator and times that by 100.
For example, 4/25*100=16%
We have to express the ratio 1 : 3.5 in the form p:q where p and q are whole numbers.
Consider the ratio of 1 and 3.5,
1 : 3.5 = 
= 
Reducing the above fraction to its lowest form.
So, we get 
Therefore, the ratio 1 : 3.5 is expressed as 
where 2 and 7 are the whole numbers.
Do you have a picture I'll show you