jmc

Let $m$ denote the number of male members and $f$ the number of female members. The sum of the ages of the female members is $40f$ and the sum of the ages of the male members is $25m$. The sum of the ages of all the members is $40f+25m$, and the total number of members is $f+m$. Since the average age for all the members is $30$, we have $$\frac{40f+25m}{f+m}=30.$$ Multiply both sides by $f+m$ to get $$40f+25m=30f+30m.$$ Collecting like terms we find $10f=5m$ so $f/m=\boxed{\frac{1}{2}}$.