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 = [tex] \frac{1}{3.5} [/tex]
= [tex] \frac{10}{35} [/tex]
Reducing the above fraction to its lowest form.
So, we get [tex] \frac{10}{35}=\frac{2}{7} [/tex]
Therefore, the ratio 1 : 3.5 is expressed as [tex] \frac{2}{7} [/tex]
where 2 and 7 are the whole numbers.