1.REAL INTEREST rate in country A is higher than B so demand for currency A is higher….and it will appreciate……
2. If INTEREST RATE(Not Real interest rate) in country A is higher, currency A will depreciate … The assumption is Real Interest rate should be same in the two countries(else money will flow to a country with higher Real interst rate) and difference in interest rate is due to inflation.The country with higher inflation,and hence higher (nominal) interest rate ,should see its currency depreciate.
3.Traders can Borrow in currecny with low interest rate(yield) and invest in “High Yielding Currencies” -both Nominal Rates-to take advantage of arbitrage whereupon interest differential and forward premium are not in agreement:
That is Interest Rate Parity ,as mandated by (1 + i$ )/(1 + iY ) = F/ S,approximated for small interest rate by, i$ − iY = (F − S)/ S ,IS VIOLATED,and taken advantage of.
Of course exchange rate is driven by demand and supply,but demand and supply is driven bymultiple factors,including Interest rates and ,trade.