1 1/4cups----------------------------->20cookies
x cups -------------------------------->12 cookies
Using cross multiplication:
[tex]\begin{gathered} 1\cdot\frac{1}{4}=\frac{4+1}{4}=\frac{5}{4} \\ \frac{5}{\frac{4}{x}}=\frac{20}{12} \\ \frac{5}{4x}=\frac{5}{3} \\ \text{solve for x:} \\ \frac{15}{20}=x \\ x=\frac{3}{4} \end{gathered}[/tex]