Two $15 \,\mathrm{cm}$ rulers retain only their $3 \,\mathrm{cm}$ and $4 \,\mathrm{cm}$ marks. They overlap facing opposite directions as shown, with one ruler’s $3 \,\mathrm{cm}$ mark aligned with the other’s $4 \,\mathrm{cm}$ mark. Find the total length $L$.
A box contains cards numbered $1$ to $7$. The first person randomly takes $3$ cards, and the second takes $2$ of the remaining cards. The first person knows for certain that the second person’s sum is even. What is the sum of the first person’s cards?
A mother distributes $17$ candies among An, Binh and Chau. An has the most and twice as many as Chau; Binh has more than Chau. How many candies does Binh have?
Today is Sunday. Minh starts a $127$-page book, reading $4$ pages daily except $25$ on Sundays. Without skipping days, on which weekday does he finish?
A rectangular vegetable plot lies in a fixed field. Extending one side by $3 m$ makes it square and reduces the bean plot by $30$ square meters. Find the original vegetable area.