I am currently taking mock economics exams but there is one question I don't know how to figure out!. 'Country x conducts 60% of its trade with country y and 40% of its trade with country z. The initial value of the trade weighted exchange rate index of country x is 100. What will be its new trade weighted exchange rate index value if its currency falls in value by 20% against the currency of y and rises by 10% against the currency of z? '... The booklet says the answer is 92 but I don't understand why? Can anybody shed some light on this for me please?

While I may argue the economic properties, this appears to be more a standard word math question.

20 percent of 60 is 12
60 minus 12 is 48
So 48 new number for country Y

10 percent of 40 is 4
40 plus 4 is 44
So 44 new numbr for country Z

48 plus 44 is 92

That is the math behind this.

Brilliant! Thanks for your help!!

it is more a simple algebra word problem. If you want to reduce it to a match equation.