Step 1: Let the numbers be in \(3:2\)
Let selected \(=3k\), unselected \(=2k\) \(⇒\) applicants \(A=5k\).
Step 2: Apply the hypothetical change
Applied \(A-100\), selected \(3k-50\). Then unselected becomes \((A-100)-(3k-50)=(2k-50)\).
Given ratio \((3k-50):(2k-50)=7:4\).
Step 3: Solve for \(k\)
\(\displaystyle \frac{3k-50}{2k-50}=\frac{7}{4}⇒ 4(3k-50)=7(2k-50)⇒ 12k-200=14k-350⇒ 2k=150⇒ k=75.\)
Hence \(A=5k=375\).
\[
\boxed{375}
\]