7. As shown in the figure, a park has two sections of road, $\mathrm{AB}=175$ meters, $\mathrm{BC}=125$ meters. On these two sections, streetlights are to be installed, with the requirement that points $\mathrm{A}$, $\mathrm{B}$, and $\mathrm{C}$ each have a streetlight, and the distance between any two adjacent streetlights is equal. Then, on these two sections of road, at least $\qquad$ streetlights need to be installed.
7. Solution: The greatest common divisor of 175 and 125 is 25, so take 25 meters as the distance between two lights, $175=25 \times 7,125=25 \times 5, AB$ segment should install $7+1=8$ lights, $BC$ segment should install $5+1$ $=6$ lights,

but at point $B$ there is no need to install a repeated light, so a total of $8+6-1=13$ (lights) are needed.