How many male competitors were there who participated in 1948 Summer?
male competitors refers to id where gender = 'M'; in 1948 Summer refers to games_name = '1948 Summer';
SELECT COUNT(T2.person_id) FROM games AS T1 INNER JOIN games_competitor AS T2 ON T1.id = T2.games_id INNER JOIN person AS T3 ON T2.person_id = T3.id WHERE T1.games_name = '1948 Summer' AND T3.gender = 'M'