There are 3 to 6 or 7 zebras in a group. Some groups come across other groups of zebras. They learn to trust each other. Soon the groups could join together to form a large herd.
Normally Zero... Usually takes a coalition of brother Cheetahs to take down a Zebra. Most Cheetahs would only go for a Sick or Injured Zebra. A loan Cheetah would not risk taking on a Zebra by itself...