Buffer cache hit very low...!!!

Hi Team,
 My OEM shows buffer cache hit ratio as 28% and library cache as 99%.
 Another query shows different results for buffer cache.
 
SQL> SELECT NAME,100-PHYSICAL_READS/(DB_BLOCK_GETS + CONSISTENT_GETS) FROM 
V$BUFFER_POOL_STATISTICS;

NAME 100-PHYSICAL_READS/(DB_BLOCK_GETS+CONSISTENT_GETS)
-------------------- --------------------------------------------------
DEFAULT 99.9072457

SQL> show sga

Total System Global Area 252273320 bytes
Fixed Size 434856 bytes
Variable Size 150994944 bytes
Database Buffers 100663296 bytes
Redo Buffers 180224 bytes

And my db_block_buffers show value as 0.

but it should be the value of database buffers / db_block_size .

SQL> show parameter db_block

NAME TYPE VALUE
------------------------------------ ----------- ----------------------
db_block_buffers integer 0
db_block_checking boolean FALSE
db_block_checksum boolean TRUE
db_block_size integer 8192

Is really my buffer cache hits very low?

 Regards - Chirag

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