答:
2^a=12,2^b=3
所以:
(2^a)/(2^b)=12/3=4
所以:2^(a-b)=2^2
所以:a-b=2
(25^a)/[5^(2b)]
=[25^a] / [25^b]
=25^(a-b)
=25^2
=625