Virender
1 - Are you using heuristic SAP_PP_019. If no then would be dynamic one.
2 - Yes netting would consider this and dynamic pegging will be created for 50qty,
Check SAP notes
393437 - Pegging in APO: background information (documentation)
458996 - Fixed pegging in SAP APO (documentation)
Specially check SAP note, point 6
448960 - Net requirements calculation (documentation)
Regards
Rahul