How did adding salt to ice change its freezing point?
The addition of salt reduces solvent-solvent interactions, and typically reduces the freezing point of the liquid.
If you live in North America, you would have seen the regular practice of salting the roads during winter in order to reduce the freezing point of water, so that the ice and frost on the roads melts, and the tyres stick to the road rather than slipping on ice.
The salting of the roads is undoubtedly the reason why so many autos in North America are absolute rust buckets. When the salty water splashes on the chassis of the auto, it serves to facilitate corrosion. I can remember one car I owned in the States that could only have been held together by rust.