In the following letter, the Rivevos Efraim discusses the question of whether one who does not say Baruch Hashem L'Olam may answer Amen when he hears the bracha. The discussion digresses into whether a Ben Chutz La'Aretz in Eretz Yisroel should say Baruch Hashem L'Olam etc.
On the reverse side of the letter, the Rivevos addresses the question of whether one needs to say Krias Shema of Ma'ariv before eating a meal. If one does not have a minyan kavu'a it is appropriate to do so:
In the last letter that I have from our correspondence, the Rivevos addresses the question of whether Chazoras HaShatz can serve as tashlumin when one missed the previous tefillah:
On the reverse side of the letter, the Rivevos discusses the question of whether an electric urn or similar appliance needs tevilah or not:
יהי זכרו ברוך