SGA_TARGET vs MAMORY_TARGET Oracle 11gR2

Hi

In a database 11g (11.2.0.1.0)

The memory parameters have this values:

memory_max_target                   big integer 48G
memory_target                            big integer 48G
pga_aggregate_target                 big integer 10G
sga_target                                   big integer 25G
pre_page_sga                             boolean     FALSE
sga_max_size                             big integer 48G

What implication has set the two parameters (memory_target and sga_target set)?.
I Know that the ideal in 11g is set sga_target = 0, but with this values what is the result?, oracle take the memory_target or sga_target?

Best Regards.