ANSWER
[tex]\frac{I_{1}}{I_{2}}=4[/tex]EXPLANATION
Let the mass of disks 1 and 2 be m.
Let the radius of disk 2 be R.
This implies that the radius of disk 1 is 2R.
The moment of inertia of disk 1 is given by:
[tex]\begin{gathered} I_1=\frac{1}{2}m(2R)^2 \\ I_1=\frac{1}{2}m*4R^2 \\ I_1=2mR^2 \end{gathered}[/tex]The moment of inertia of disk 2 is given by:
[tex]I_2=\frac{1}{2}mR^2[/tex]Therefore, the ratio of the moment of inertia of disk 1 to disk 2 is:
[tex]\begin{gathered} \frac{I_1}{I_2}=\frac{2mR^2}{\frac{1}{2}mR^2} \\ \frac{I_1}{I_2}=\frac{2}{\frac{1}{2}}=2*2 \\ \frac{I_1}{I_2}=4 \end{gathered}[/tex]That is the answer.
