21% adults favor the use of unmanned drones by police agencies. Twelve U. S. adults are randomly selected. Find the probability that the number of U. S. adults who favor the use of unmanned drones by police agencies is (a) exactly three, (b) at least four, (c) less than eight

a)

b)

And we can find the individual probabilities:

And replacing we got:

c)

And replacing we got:

Step-by-step explanation:

Let X the random variable of interest "number of US adults who favor the use of unmanned drones", on this case we now that:

The probability mass function for the Binomial distribution is given as:

Where (nCx) means combinatory and it's given by this formula:

Part a

Part b

We want to find this probability:

And we can use the complement rule and we got:

And we can find the individual probabilities:

And replacing we got:

Part c

We want this probability:

And using the complement rule got:

And we have this:

And replacing we got:

  or  

step-by-step explanation:

if the four friends split the cost, p, of the pizza evenly, then each friend pays one-fourth of the cost of the pizza.

the expression is   or  

the answer is 8/21

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