A3. One person can make $n$ objects in an hour. Ann begins at 10:00 AM, Bob begins at 10:20 AM, then Cody and Deb begin at 10:40 AM. Working at the same constant speed, by 11:00 AM, they have made 28 objects. What is $n$ ?
Solution: At $11 \mathrm{am}$, Ann has worked for 1 hour, Bob has worked for $\frac{2}{3}$ of an hour, and both Cody and Deb have worked for $\frac{1}{3}$ of an hour. Together, they have worked for $1+\frac{2}{3}+\frac{2}{3}=\frac{7}{3}$ hours. Thus, $n=28 \div \frac{7}{3}=12$.
Answer: 12