Change : \(1\dfrac{1}{2}=\dfrac{3}{2}\)

Call that number is a 

We have : 

\(a+\dfrac{3}{2}=\dfrac{3}{2}a\)

\(\Rightarrow\dfrac{3}{2}=\dfrac{1}{2}a\)

\(\Rightarrow a=\dfrac{3}{2}:\dfrac{1}{2}\)

\(\Rightarrow a=3\)

So that number is 3