RDA - Top SQL report

Hi,
 
The question is regarding (Remote Diagnostics Assistant; Metalink Note: 
314422.1) Oracle Support provides to troubleshoot performance issues in a 
database {RDA} and the calculation of the "Top SQL Report"
 
More specifically, I am curious how the following ratios are deemed "Expected 
Respose Time (in Seconds)"
 
From v$sqlarea:
 { (disk_reads/executions)/50 }
 { (buffer_gets/executions)/500 }
 
Also, what is the significance of the numbers 50 and 500 respectively?
 
Queries used in the report:
 
select
 sql_text, 
 executions,
 disk_reads / decode(executions,0,1, executions) / 50
from
 v$sqlarea
where  
 disk_reads / decode(executions,0,1, executions) / 50 > 100
order  by executions desc;

select
 sql_text, 
 executions,
 buffer_gets / decode(executions,0,1, executions) / 500
from
 v$sqlarea
where  
 buffer_gets/ decode(executions,0,1, executions) / 500 > 100
order  by executions desc;
 
Thanks,
Sri
 
 
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