Answer:
The probability is [tex]0.0228[/tex]
Step-by-step explanation:
Let's start by defining the random variable [tex]G[/tex] as :
[tex]G:[/tex] '' The amount of gasoline sold each month to customers at Bob's Exxon station in downtown Navasota ''
Therefore, if [tex]X[/tex] is a continuous random variable that has a normal distribution, we write [tex]X[/tex] ~ [tex]N[/tex] ( μ , σ )
Where ''μ'' is the mean and ''σ'' is the standard deviation.
For the random variable [tex]G[/tex] we write :
[tex]G[/tex] ~ [tex]N(2500,250)[/tex]
We need to find [tex]P(G>3000)[/tex]
In order to calculate this, we are going to standardize the variable. This means, finding the equivalent probability in a normal random variable
[tex]Z[/tex] ~ [tex]N(0,1)[/tex]
We perform this because the random variable [tex]Z[/tex] ~ [tex]N(0,1)[/tex] is tabulated in any book or either you can find the table on Internet.
To standardize the variable we need to subtract the mean and then divide by the standard deviation ⇒
[tex]P(G>3000)[/tex] ⇒ P[ (G - μ) / σ > [tex]\frac{3000-2500}{250}[/tex] ] ⇒ [tex]P(Z>2)[/tex]
Because (G - μ) / σ ~ [tex]Z[/tex]
Finally, [tex]P(G>3000)=P(Z>2)[/tex] ⇒ [tex]P(Z>2)=1-P(Z\leq 2)[/tex] = 1 - Φ(2)
Where '' Ф(x) = [tex]P(X\leq x)[/tex] '' represents the cumulative function of [tex]Z[/tex]
Looking for Φ(2) in any table,
[tex]P(G>3000)=P(Z>2)=1-P(Z\leq 2)=1-0.9772=0.0228[/tex] ≅ %2.28
We found out that the probability is [tex]0.0228[/tex]
