Answer:

And using the cdf we got:

Step-by-step explanation:
Previous concepts
The exponential distribution is "the probability distribution of the time between events in a Poisson process (a process in which events occur continuously and independently at a constant average rate). It is a particular case of the gamma distribution". The probability density function is given by:

And 0 for other case. Let X the random variable that represent the random variable of interest and we know that the distribution is given by:

We know the variance on this case given by :

So then the deviation is given by:

And if we solve for
we got:

The cumulative distribution function for the exponential distribution is given by:

Solution to the problem
And for this case we want to find this probability:

And using the cdf we got:

Since 32 mil is 1/10 of the US pop, multiply 32 mil by 10 so you get the 10/10 aka the whole US pop. That means it would be 320,000,000. All you do is add a zero to 32 mil since you multiply by 10. 32 mil originally had 6 zeros. After multiplying, you have 7 zeros.
D = 20
.....................................
The denominator tells you the total amount of pieces.
Answer:
b
Step-by-step explanation: