1. -1
2. 1/2
not sure:
3. 7? —> 7x 1/7x=7x1= 7
4. 1/11?
Answer:
4 stations
Step-by-step explanation:
If we need to be at least 98% certain that an enemy plane flying over will be detected by at least one station, we must ensure that there is at most a 2% chance that no radar stations detect the plane.
The probability that a single radar station does not detect the plane is 0.35.
For n radar stations:

Rounding up to the next whole station, at least 4 stations are needed.