A salt of formula $\mathrm{AB_2}$ has a molar solubility of $1.0 \times 10^{-2}$ M. Compute its solubility product, in units of $10^{-6}$.

4 (answers within ±0.2 count)

$K_{sp} = [A][B]^2 = s(2s)^2 = 4s^3 = 4 \times (10^{-2})^3 = 4 \times 10^{-6}$. Forgetting either the doubling or the squaring is the classic error, and each one changes the answer by a factor of four.