In a recent survey it was found that Americans drink an average of 23.2 gallons of bottled water in a year. If the standard deviation is 2.7 gallons and the variable is normally distributed, find the probability that a randomly selected American drinks more than 25 gallons of bottled water in a year. What is the probability that the selected person drinks between 22 and 30 gallons

Answer:

a) 0.25249

b) 0.66575

Step-by-step explanation:

We solve this question using z score formula

= z = (x-μ)/σ, where

x is the raw score

μ is the population mean = 23.2 gallons

σ is the population standard deviation = 2.7 gallons

a) Find the probability that a randomly selected American drinks more than 25 gallons of bottled water in a year.

For x = 25 gallons

z = 25 - 23.2/2.7

z = 0.66667

Probability value from Z-Table:

P(x<25) = 0.74751

P(x>25) = 1 - P(x<25)

1 - 0.74751

= 0.25249

The probability that a randomly selected American drinks more than 25 gallons of bottled water in a year is 0.25249

2) What is the probability that the selected person drinks between 22 and 30 gallons

For x = 22 gallons

z = 22 - 23.2/2.7

z = -0.44444

Probability value from Z-Table:

P(x = 22) = 0.32836

For x = 30 gallons

z = 30 - 23.2/2.7

z =2.51852

Probability value from Z-Table:

P(x = 30) = 0.99411

The probability that the selected person drinks between 22 and 30 gallons is

P(x = 30) - P(x = 22)

= 0.99411 - 0.32836

= 0.66575

Final answer:

The probability that a randomly selected American drinks more than 25 gallons of bottled water in a year is approximately 0.2514, while the probability that they will drink between 22 and 30 gallons is approximately 0.6643.

Explanation:

This is a statistics question about probability distribution, specifically, normal distribution. You need to find the z-scores and use the standard normal distribution table to find the probabilities.

The average or mean (μ) consumption is 23.2 gallons and standard deviation (σ) is 2.7 gallons.

First, we use the z-score formula: z = (X - μ) / σ

To find out the probability that a selected American drinks more than 25 gallons annually, we substitute X = 25, μ = 23.2 and σ = 2.7 into the z-score formula to get z = (25 - 23.2) / 2.7 ≈ 0.67. Z value of 0.67 corresponds to the probability of 0.7486 in standard normal distribution table, but this is the opposite of what we want. We need to subtract this probability from 1 to find the probability that a person drinks more than 25 gallons annually. So 1 - 0.7486 = 0.2514.

Second, to find the probability an individual drinks between 22 and 30 gallons, we calculate two z-scores: For X = 22, z = (22 - 23.2) / 2.7 ≈ -0.44 with corresponding probability 0.3300, and for X = 30, z = (30 - 23.2) / 2.7 ≈ 2.52 with corresponding probability 0.9943. We find the probability of someone drinking between these quantities by subtracting the smaller probability from the larger, 0.9943 - 0.3300 = 0.6643.

Learn more about Normal Distribution here:

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