17.Last week,the exchange rate of Australian dollars to Hong Kong dollars was
AUS $1=HK$5.This week is AUS$1=$4.5.
a)Find the percentage decrease of the exchange of Australian dollars to Hong Kong dollars.
b)Daniel has AUS $1 000.If he wants to get more Hong Kong dollars,shoud he exchange the money last week or this week?What is the difference between the two?