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a researcher measures the amount of sugar in several cans of the same soda. The mean is 39.01 with a standard deviation of .5. the researcher randomly selects a sample of 100.
a) find the probability that the sum of the 100 values is greater than 3,910
b) find the probability that the sum of the 100 values is less than 3,900
c) find the probability that the sum of the 100 values falls between the numbers you found in parts (a) and (b)
d) find the probability that the sums will fall between the z-scores of -2 and 1


Sagot :

Answer:

Step-by-step explanation:

To address these questions, we'll use the properties of the sum of normally distributed variables. Given that the mean of the sugar amount is \( \mu = 39.01 \) and the standard deviation is \( \sigma = 0.5 \), each can's sugar content can be considered normally distributed.

For a sample of 100 cans:

- The mean of the sum \( S_{100} \) of these 100 cans is \( \mu_{S_{100}} = 100 \times 39.01 = 3901 \).

- The standard deviation of the sum \( S_{100} \) is \( \sigma_{S_{100}} = \sqrt{100} \times 0.5 = 5 \).

Now, let's calculate the probabilities:

**a) Probability that the sum of the 100 values is greater than 3,910:**

Convert this to a standard normal variable \( Z \):

\[ Z = \frac{3910 - 3901}{5} = \frac{9}{5} = 1.8 \]

Now, find the probability \( P(Z > 1.8) \) using the standard normal distribution table or calculator:

\[ P(Z > 1.8) \approx 0.0359 \]

**b) Probability that the sum of the 100 values is less than 3,900:**

Convert this to a standard normal variable \( Z \):

\[ Z = \frac{3900 - 3901}{5} = -0.2 \]

Now, find the probability \( P(Z < -0.2) \):

\[ P(Z < -0.2) \approx 0.4207 \]

**c) Probability that the sum of the 100 values falls between the numbers found in parts (a) and (b):**

This is \( P(3900 < S_{100} < 3910) \). Using the standard normal probabilities from parts (a) and (b):

\[ P(3900 < S_{100} < 3910) = 1 - [P(Z \leq -0.2) + P(Z \geq 1.8)] \]

\[ P(3900 < S_{100} < 3910) = 1 - [0.4207 + 0.0359] \]

\[ P(3900 < S_{100} < 3910) \approx 1 - 0.4566 \]

\[ P(3900 < S_{100} < 3910) \approx 0.5434 \]

**d) Probability that the sum of the 100 values falls between the z-scores of -2 and 1:**

Convert -2 and 1 to standard normal variables:

For \( Z = -2 \):

\[ P(Z < -2) \approx 0.0228 \]

For \( Z = 1 \):

\[ P(Z < 1) \approx 0.8413 \]

Now, find \( P(-2 < Z < 1) \):

\[ P(-2 < Z < 1) = P(Z < 1) - P(Z < -2) \]

\[ P(-2 < Z < 1) = 0.8413 - 0.0228 \]

\[ P(-2 < Z < 1) = 0.8185 \]

Therefore, the probabilities for the scenarios described are:

- **a)** Probability \( P(S_{100} > 3910) \approx 0.0359 \)

- **b)** Probability \( P(S_{100} < 3900) \approx 0.4207 \)

- **c)** Probability \( P(3900 < S_{100} < 3910) \approx 0.5434 \)

- **d)** Probability \( P(-2 < Z < 1) \approx 0.8185 \)