well basically, the terms of trade is a relationship between the price of a country's imports relative to the price of exports
the index is given as X price index/M price index x 100
if anything, ull get a multiple guess or short answer on it, so all u gotta realli kno is that wen import prices increase relative to export prices, our terms of trade has deteriorated ...and when export prices increase relative to import prices, terms of trade improve
trade weighted index is the mesurement of, say Aust.'s currency against the currencies of all our major trading partner's with out most major partners given a higher weighting...its like an effective exchange rate that uses value of imports and exports to determine the index.
both these relate to the CAD by...something like if our terms of trade is deteriorating, theres more pressure on CAD and therefore external instability...same with TWI...if our TWI decreases, external stability worsens
the reasons as to why should b in ur text book