TITLE: Is it true that $\text{Ext}(A,\Bbb Z)=\text{Ext}(A_{tor},\Bbb Z)$ for any abelian group $A$?
QUESTION [5 upvotes]: Is it true that $\text{Ext}(A,\Bbb Z)=\text{Ext}(A_{tor},\Bbb Z)$ for any abelian group $A$? Obviously this is true when $A$ is finitely generated, since $\text{Ext}(G,\Bbb Z)=0$ if $G$ is free. But I'm curious that whether or not this is true in the general case.

REPLY [4 votes]: Take $A = \mathbb Q$, since it is torsion free we have $\mathsf{Ext}(\mathbb Q_{\mathsf{tors}}, \mathbb Z) = 0$, but $\mathsf{Ext}(\mathbb Q,\mathbb Z) \neq 0$. See here.