Third one down
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Answer:
The probability that 8 mice are required is 0.2428.
Step-by-step explanation:
Given : A scientist inoculates mice, one at a time, with a disease germ until he finds 3 that have contracted the disease. If the probability of contracting the disease is two sevenths.
To find : What is the probability that 8 mice are required? The probability that that 8 mice are required is nothing ?
Solution :
Applying binomial distribution,

Where, p is the probability of success 
q is the probability of failure q=1-p, 
n is total number of trials n=8
r=3
Substitute the values,




Therefore, the probability that 8 mice are required is 0.2428.
The larger number is (-7+14)/2 = 3.5.
The smaller number is (-7-14)/2 = -10.5.
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The two equations a+b=-7, a-b=14 can be solved to get these results. It is genrally convenient to solve them by adding one to the other, or subtracting one from the other.
Answer:

You can plug it into a graphing website or calculator to double check