Answer:
The correct answer is option 'a' : 120 is more than 2.5 standard deviations above the expected value.
Step-by-step explanation:
For an exponential distribution we have
The expected value μ = 80
No of trails n = 200
Thus we have

The deviation is related to expected value and probability as

Thus the values between the given deviation is

Now since 120 successes are out of the range of [62.75,97.25] thus 120 is more than the expected value.
Answer:
1008
Step-by-step explanation:
If 4/5 of eighth graders, or 80%, are enrolled with class, there are still 20% of students that didn't study. That means you add 168, the 20%, and you'll get 1008.