Let x be the number of men.
Then the number of women is (50-x).
Following the condition, you may write the proportion
= = .
From the proportion
7x = 3*(50-x).
Simplify and solve
7x = 150 - 3x
7x + 3x = 150
10x = 150
x = 150/10 = 15.
ANSWER. 15 men and (50-15) = 35 women.