(a) The duplicate ratio of `1 : ab " is " (1)^(2) : (ab)^(2) = 1 : a^(2)b^(2)`

Hence the given statement is true .

(b) The sub- duplicate ratio of ` 4 : 9 " is " sqrt(4) : sqrt(9) = 2 : 3 , ` which is not equal to ` 3 : 2` .

Hence the given statement is false.