On Monday, Krikor left his house at 8:00 a.m., drove at a constant speed, and arrived at work at 8:30 a.m. On Tuesday, he left his house at 8:05 a.m., drove at a constant speed, and arrived at work at 8:30 a.m. By what percentage did he increase his speed from Monday to Tuesday?
Let $v_{1} \mathrm{~km} / \mathrm{h}$ be Krikor's constant speed on Monday.

Let $v_{2} \mathrm{~km} / \mathrm{h}$ be Krikor's constant speed on Tuesday.

On Monday, Krikor drives for 30 minutes, which is $\frac{1}{2}$ hour.

Therefore, on Monday, Krikor drives $\frac{1}{2} v_{1} \mathrm{~km}$.

On Tuesday, Krikor drives for 25 minutes, which is $\frac{5}{12}$ hour.

Therefore, on Tuesday, Krikor drives $\frac{5}{12} v_{2} \mathrm{~km}$.

Since Krikor drives the same distance on both days, then $\frac{1}{2} v_{1}=\frac{5}{12} v_{2}$ and so $v_{2}=\frac{12}{5} \cdot \frac{1}{2} v_{1}=\frac{6}{5} v_{1}$. Since $v_{2}=\frac{6}{5} v_{1}=\frac{120}{100} v_{1}$, then $v_{2}$ is $20 \%$ larger than $v_{1}$.

That is, Krikor drives $20 \%$ faster on Tuesday than on Monday.

ANSWER: $20 \%$