"__ cups in a pint?" or "A Bakers Dozen is __".
Indeed, it will be really fun to g2google before every comment just so I can find out these values. Some people are still sticking with metric system, some - with Imperial. Also, there is a limited amount of "cups in a pint" variations that can be put in a CAPTCHA system (since these have to be human generated), so it will not take too long to write an automatic solver of this problem. Therefore, while the CAPTCHAS of today are vulnerable to solutions of cheap workforce, this is actually vulnerable to automatic solving, which is way worse.
Love may laugh at locksmiths, but he has a profound respect for money bags. -- Sidney Paternoster, "The Folly of the Wise"