2 Formatted code to make it easier to copy / paste
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In[3]:= Classify["Sentiment", "I love this book.", "Probabilities"]["Positive"]
Out[3]=(* Out: 0.728592 *)

In[4]:= %*100
Out[4]=(* Out: 72.8592 *)
In[3]:= Classify["Sentiment", "I love this book.", "Probabilities"]["Positive"]
Out[3]= 0.728592

In[4]:= %*100
Out[4]= 72.8592
Classify["Sentiment", "I love this book.", "Probabilities"]["Positive"]
(* Out: 0.728592 *)

%*100
(* Out: 72.8592 *)
1
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In[3]:= Classify["Sentiment", "I love this book.", "Probabilities"]["Positive"]
Out[3]= 0.728592

In[4]:= %*100
Out[4]= 72.8592