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Calculate the probabilities for selecting bats with specific weights from a normally distributed population.

Mathematics

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Answers

2 parts
i
0.8400
ii
0.0001

Step-by-step solution

4 steps

Here's how to solve the probability problem:

Step 1: Identify the given information.
Mean weight, μ=1.25 grams\mu = 1.25 \text{ grams}
Standard deviation, σ=0.25 grams\sigma = 0.25 \text{ grams}
The weights are normally distributed.

Part i· 2 steps

Probability of randomly selecting a bat that weighs between 1 gram and 2 grams

  1. Convert the weights to Z-scores.

    For X1=1 gramX_1 = 1 \text{ gram}:

    Z1=X1−μσ=1−1.250.25=−0.250.25=−1.00Z_1 = \frac{X_1 - \mu}{\sigma} = \frac{1 - 1.25}{0.25} = \frac{-0.25}{0.25} = -1.00

    For X2=2 gramsX_2 = 2 \text{ grams}:

    Z2=X2−μσ=2−1.250.25=0.750.25=3.00Z_2 = \frac{X_2 - \mu}{\sigma} = \frac{2 - 1.25}{0.25} = \frac{0.75}{0.25} = 3.00
  2. Find the probability using the Z-scores.

    We need to find P(1<X<2)P(1 < X < 2), which is equivalent to P(−1.00<Z<3.00)P(-1.00 < Z < 3.00).
    Using a standard normal distribution table (Z-table):
    P(Z<3.00)=0.9987P(Z < 3.00) = 0.9987
    P(Z<−1.00)=0.1587P(Z < -1.00) = 0.1587

    P(−1.00<Z<3.00)=P(Z<3.00)−P(Z<−1.00)P(-1.00 < Z < 3.00) = P(Z < 3.00) - P(Z < -1.00) P(−1.00<Z<3.00)=0.9987−0.1587P(-1.00 < Z < 3.00) = 0.9987 - 0.1587 P(−1.00<Z<3.00)=0.8400P(-1.00 < Z < 3.00) = 0.8400

    The probability is:

    0.8400\boxed{0.8400}

Part ii0.0001

Probability of randomly selecting a bat that weighs more than 2.2 grams

  1. Convert the weight to a Z-score.

    For X=2.2 gramsX = 2.2 \text{ grams}:

    Z=X−μσ=2.2−1.250.25=0.950.25=3.80Z = \frac{X - \mu}{\sigma} = \frac{2.2 - 1.25}{0.25} = \frac{0.95}{0.25} = 3.80
  2. Find the probability using the Z-score.

    We need to find P(X>2.2)P(X > 2.2), which is equivalent to P(Z>3.80)P(Z > 3.80).
    Using a standard normal distribution table (Z-table):
    P(Z>3.80)=1−P(Z<3.80)P(Z > 3.80) = 1 - P(Z < 3.80)
    P(Z<3.80)≈0.9999P(Z < 3.80) \approx 0.9999 (since 3.80 is a very high Z-score)

    P(Z>3.80)=1−0.9999P(Z > 3.80) = 1 - 0.9999 P(Z>3.80)=0.0001P(Z > 3.80) = 0.0001

    The probability is:

    0.0001\boxed{0.0001}
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