Passage: Comparisons of national income are also frequently made on the basis of purchasing power parity (PPP), to adjust for differences in the cost of living in different countries. (See List of countries by GDP (PPP) per capita.) PPP largely removes the exchange rate problem but not others; it does not reflect the value of economic output in international trade, and it also requires more estimation than GDP per capita. On the whole, PPP per capita figures are more narrowly spread than nominal GDP per capita figures.

Question: What is the only problem that PPP solves?
the exchange rate problem