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An engineer is going to redesign an ejection seat for an airplane. The seat was designed for pilots weighing between 120 lb and 181 lb. The new population of pilots has normally distributed weights with a mean of 128 lb and a standard deviation of 32.4 lb.

If a pilot is randomly selected, find the probability that his weight is between 120 lb and 181 lb.

The probability is approximately __. (Round to four decimal places as needed.)

Answer :

Using the Z-score formula and a standard normal distribution table, the probability that a randomly selected pilot's weight is between 120 lb and 181 lb, given a normal weight distribution with a mean of 128 lb and a standard deviation of 32.4 lb, is approximately 0.5469 or 54.69%.

To calculate the probability that a randomly selected pilot's weight is between 120 lb and 181 lb, given a normal distribution with a mean of 128 lb and a standard deviation of 32.4 lb, we will use the Z-score formula. The Z-score is given by Z = (X - mean) / (standard deviation), where X is the value for which we are finding the Z-score.


For X = 120 lb (the lower limit),
Z1 = (120 - 128) / 32.4 = -0.2469 (approximately).
For X = 181 lb (the upper limit),
Z2 = (181 - 128) / 32.4 = 1.6358 (approximately).

Using a standard normal distribution table or a calculator, we can find the area (probability) to the left of Z1 and the area to the left of Z2. Subtracting these gives us the probability that the weight is between 120 lb and 181 lb:

[tex]P(Z1 < Z < Z2) = P(Z < Z2) - P(Z < Z1)[/tex]

By looking up Z1 and Z2 in a Z-table or using an online calculator:

  • P(Z < -0.2469)
    = 0.4026 (approximately)
  • P(Z < 1.6358)
    = 0.9495 (approximately)


Therefore, the probability that a randomly selected pilot weighs between 120 lb and 181 lb is:


0.9495 - 0.4026 = 0.5469


Rounded to four decimal places, the probability is 0.5469, or approximately 54.69%.

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