The mean of 10 numbers is 20. Five of them have mean 16. What is the mean of the other five?

All ten numbers total $10\times 20=200$ and the first five total $5\times 16=80$, so the other five total 120 and their mean is 120 ÷ 5 = 24. Because the two halves are equally large, the overall mean 20 sits exactly midway between 16 and 24 — a shortcut that would fail if the two groups had different sizes.