一个国际象棋俱乐部目前有 37 名男会员和 16 名女会员。该俱乐部举办了一次情人节活动，以吸引已婚夫妇作为新会员加入俱乐部。（夫妻双方必须都是该俱乐部的新会员。）在这次活动之后，女会员的比例变为了 40%。求活动后加入俱乐部的已婚夫妇数量。

1. Define the unknown and express the new numbers of male, female and total members.

Let the number of married couples who joined be $x$.

Since each couple has one husband and one wife,

New number of female members $=16+x$.

New total number of members $=37+16+2x=53+2x$.

2. Form an equation using the given female percentage.

After the event, female members made up $40\%$ of the club.

$\frac{16+x}{53+2x}=40\%=\frac{40}{100}=\frac{2}{5}$

3. Solve the linear equation for the number of couples.

$5(16+x)=2(53+2x)$

$80+5x=106+4x$

$x=26$

This gives $x=26$, but this is not consistent with the percentage increasing from $\frac{16}{53}\approx30.2\%$ to $40\%$? Check the algebra:

$80+5x=106+4x \Rightarrow x=26$

So $26$ married couples joined.