[Algebra]
Problem: Let $A=\frac{1}{9}$, and let $B=\frac{1}{25}$. In $\frac{1}{A}$ minutes, 20 frogs can eat 1800 flies. At this rate, in $\frac{1}{B}$ minutes, how many flies will 15 frogs be able to eat?

Solution: In $\frac{1}{A}$ minutes, 1 frog can eat $1800 / 20=90$ flies; thus in $\frac{1}{B}$ minutes, 1 frog can eat $\frac{A}{B} \cdot 90$ flies. Thus in $\frac{1}{B}$ minutes, 15 frogs can eat $15 \cdot 90 \cdot \frac{A}{B}$ flies. With $A=\frac{1}{9}$ and $B=\frac{1}{25}$, this simplifies to $15 \cdot 250=\mathbf{3 7 5 0}$.

Final answer: 3750