solution: Because $\triangle RST$ is a right triangle, $\sin R = \frac{ST}{RT}$. So $\sin R = \frac{2}{5} = \frac{ST}{5}$. Then $ST=2$.
  
  We know that $\sin T = \frac{RS}{RT}$. By the Pythagorean Theorem, $RS = \sqrt{RT^2 - ST^2} = \sqrt{25-4} = \sqrt{21}$. Then $\sin T = \boxed{\frac{\sqrt{21}}{5}}$.
prompt.content: <|im_start|>system
  You are a helpful assistant.<|im_end|>
  <|im_start|>user
  In $\triangle{RST}$, shown, $\sin{R}=\frac{2}{5}$.  What is $\sin{T}$?
  
  [asy]
  pair R,S,T;
  T = (0,0);
  S = (2,0);
  R = (2,sqrt(21));
  draw(R--S--T--R);
  draw(rightanglemark(R,S,T,10));
  label("$T$",T,SW);
  label("$S$",S,SE);
  label("$R$",R,NE);
  label("$5$",(R+T)/2,NW);
  [/asy]
  Please reason step by step, and put your final answer within \boxed{{}}.<|im_end|>
  <|im_start|>assistant
  
prompt.role: user
extra_info.answer: \frac{\sqrt{21}}{5}
extra_info.question: In $\triangle{RST}$, shown, $\sin{R}=\frac{2}{5}$.  What is $\sin{T}$?
  
  [asy]
  pair R,S,T;
  T = (0,0);
  S = (2,0);
  R = (2,sqrt(21));
  draw(R--S--T--R);
  draw(rightanglemark(R,S,T,10));
  label("$T$",T,SW);
  label("$S$",S,SE);
  label("$R$",R,NE);
  label("$5$",(R+T)/2,NW);
  [/asy]
extra_info.split: test