Answer:
0.36427
Step-by-step explanation:
Mean = λ = 18 messages per hour
P(X = x) = (e^-λ)(λ⁻ˣ)/x!
P(X ≤ x) = Σ (e^-λ)(λ⁻ˣ)/x! (Summation From 0 to x)
But the probability required is that the messages thay come in an hour is between 15 and 20, that is, P(15 < X < 20)
P(15 < X < 20) = P(X < 20) - P(X ≤ 15)
These probabilities will be evaluated using a cumulative frequency calculator.
P(X < 20) = 0.65092
P(X ≤ 15) = poissoncdf(18, 15) = 0.28665
P(15 < X < 20) = P(X < 20) - P(X ≤ 15) = 0.65092 - 0.28665 = 0.36427.
You can use the Poisson distribution calculator here
https://stattrek.com/online-calculator/poisson.aspx
10^-10 in decimal form is 0.000000001. Because the exponent is negative, you move the decimal point ( decimal point is at the end of 0 of the base number 10) 10 place to the right of 10 and u get the answer above. I discarded the 0 later in the answer because now that you've moved the decimal, that 0 have no value. But when forming it in decimal you have to use that 0 or you will get a wrong answer, instead of eight 0's, you will end up with nine 0's.
Skylar went 13ft per second
Rodrigo went 13 1/2 ft per second
So, 1/2 a ft per second
