Answer: Our required probability is 0.3387.
Step-by-step explanation:
Since we have given that
Number of red cards = 4
Number of black cards = 5
Number of cards drawn = 5
We need to find the probability of getting exactly three black cards.
Probability of getting a black card = 
Probability of getting a red card = 
So, using "Binomial distribution", let X be the number of black cards:

Hence, our required probability is 0.3387.
4/5 recommend, so about 4/5(120) = 96 doctors recommend the brand.
Answer:
d≈7.07
Step-by-step explanation:
Using the formulas
P=4a
d= \sqrt{2} a
Solving ford
d= \sqrt{2} P/4=2·20
/4≈7.07107
The answer is Y=34
Because 34/17 is 34