The article explores how changes in interest rates affect economic growth and welfare in two countries. Higher domestic interest rates lead to less investment in research and development, slowing down technology growth. When each country sets its own interest rates, they end up higher than if they worked together. This is because of how trade between countries affects monetary policy. The study also shows that market power of firms can impact the difference between actual and ideal interest rates. The findings suggest that the effects of monetary policy on welfare can be significant across countries.