SCHEMA:
CREATE TABLE table_name_80 (number_of_electorates__2003_ INTEGER, reserved_for___sc___st__none_ VARCHAR, constituency_number VARCHAR)
USER:
What is the average number of electorates (2003) reserved for sc with a constituency number of 50?

QUERY:
SELECT AVG(number_of_electorates__2003_) FROM table_name_80 WHERE reserved_for___sc___st__none_ = "sc" AND constituency_number = "50"