Thread: True/False probability questions

No idea about the first two, but i think 3 is true, 4 is tru, and 5 is false :S can sum1 help me out

1) The amount of petrol purchased at a local service station per car has a normal distribution with a population mean of 45L with a population standard deviation of 5.3L.

99% of cars will purchase between 32.651L and 57.349L.

a. True
b. False

2) The amount of petrol purchased at a local service station per car has a normal distribution with a population mean of 45L with a population standard deviation of 5.3L.

If data is collected for a random sample of 4 cars, there is approximately a 97.06% chance that the sample mean will be between 40 and 45L.

a. True
b. False

3) As the sample size increases, the effect of an extreme value on the sample mean becomes smaller.

a. True
b. False

4) If a population distribution is unimodal and skewed, in most cases the sampling distribution of the mean can be approximated by the normal distribution if the samples contain at least 20 observations.

a. True
b. False

5) If the population distribution is symmetric (but not unimodal), the sampling distribution of the mean can be approximated by the standard normal distribution as long as the samples contain at least 20 observations.

a. True
b. False

1.False...
Other questions i will check later.

do u think u could check the others now?

Originally Posted by vijanator

No idea about the first two, but i think 3 is true, 4 is tru, and 5 is false :S can sum1 help me out

1) The amount of petrol purchased at a local service station per car has a normal distribution with a population mean of 45L with a population standard deviation of 5.3L.

99% of cars will purchase between 32.651L and 57.349L.

a. True
b. False

2) The amount of petrol purchased at a local service station per car has a normal distribution with a population mean of 45L with a population standard deviation of 5.3L.

If data is collected for a random sample of 4 cars, there is approximately a 97.06% chance that the sample mean will be between 40 and 45L.

a. True
b. False

3) As the sample size increases, the effect of an extreme value on the sample mean becomes smaller.

a. True
b. False

4) If a population distribution is unimodal and skewed, in most cases the sampling distribution of the mean can be approximated by the normal distribution if the samples contain at least 20 observations.

a. True
b. False

5) If the population distribution is symmetric (but not unimodal), the sampling distribution of the mean can be approximated by the standard normal distribution as long as the samples contain at least 20 observations.

a. True
b. False

1) You're expected to be able to calculate Pr(32.651 < X < 57.349) when X follows a normal distribution with the given mean and sd. The answer is false. The calculation is left for you to do using what you should have been taught in class.

2) You're expected to know that the sample mean Xbar follows a normal distribution with mean 45 and sd 5.3/sqrt{4} = 2.65. Calculate Pr(40 < Xbar < 45). Is it equal to 0.9706?

3) - 5) ought to be able to be answered by refering to your class notes or textbook and reviewing the relevant material.