The distribution of water fleas (Daphnia) in a given water pond is fairly random and the population density is fairly constant. The average number of water fleas caught by sweeping the water a single time with a standard net is 3.7 individuals. If tomorrow a net will be used once in the pond what is the probability of catching: a) 5 individuals?b) at least 2 individuals?

Respuesta :

Answer:

(a) The probability of catching 5 individuals in the pond is 0.1429.

(b) The probability of catching at least 2 individuals in the pond is 0.8838.

Step-by-step explanation:

Let X = number of water fleas caught by sweeping the water a single time.

The random variable X follows a Poisson distribution with parameter λ = 3.7.

The probability mass function of the Poisson distribution is:

[tex]P(X=x)=\frac{e^{-3.7}3.7^{x}}{x!}[/tex]

(a)

Compute the value of P (X = 5) as follows:

[tex]P(X=5)=\frac{e^{-3.7}3.7^{5}}{5!}=\frac{17.1443}{120} =0.142869\approx0.1429[/tex]

Thus, the probability of catching 5 individuals in the pond is 0.1429.

(b)

Compute the value of P (X ≥ 2) as follows:

P (X ≥ 2) = 1 - P (X < 2)

              = 1 - P (X = 0) - P (X = 1)

              [tex]=1-\frac{e^{-3.7}3.7^{0}}{0!}-\frac{e^{-3.7}3.7^{1}}{1!}\\=1-0.0247-0.0915\\=0.8838[/tex]

Thus, the probability of catching at least 2 individuals in the pond is 0.8838.