Question 283354
What do we know?
<ul><li>Math Club students make up 80% (0.8) of the Science Club.
<li> The Science Club has 15 members, so 
{{{15 * 0.8 = 12}}}<br>
<li>Science Club members make up 30% (0.3) of the Math Club.
We'll let "M" stand for the Math Club Membership.<br>
{{{0.3M = 12}}}<br>
Divide both sides by 30% (0.3):
{{{0.3M/0.3 = 15/0.3}}}<br></ul>
M = 40 and bob's your uncle!