Randomness Probability

A random variable X has a mean of 5 and a st. dev of 0.40. A random variable Y has a mean of 8 and a st. dev of 0.60. If both are independent, what is the st. dev of X - Y?

• 0.52

• 0.72

• 1.0

• Not here

Use your turn signals!
If 20% of drivers do not use turn signals, given an SRS of 4 drivers, what's the probability that at least one does not use turn signals?

• (.2)⁴

• (.8)⁴

• 4(.2)(.8)³

• 4(.2)³(.8)

One brand of a baby bathtub comes with a dial to set the water temperature. When the "babysafe" setting is selected and the tub is filled, the temperature X of the water in a randomly selected bath follows a Normal distribution with a mean of 34°C and a standard deviation of 2°C. Let Y be the water temperature in degrees Fahrenheit for the randomly selected bath. Recall that F=9/5C+32. Calculate and interpret the mean and standard deviation of Y.

• μ_Y=93.2°F and σ_Y=35.6°F. When the dial is set to "babysafe," the temperature of a randomly selected bath typically varies about 35.6°F from the mean of 93.2°F.

• μ_Y=93.2°F and σ_Y=3.6°F. When the dial is set to "babysafe," the temperature of a randomly selected bath typically varies about 3.6°F from the mean of 93.2°F.

• μ_Y=61.2°F and σ_Y=3.6°F. When the dial is set to "babysafe," the temperature of a randomly selected bath typically varies about 3.6°F from the mean of 61.2°F.

• μ_Y=93.2°F and σ_Y=12.96°F. When the dial is set to "babysafe," the temperature of a randomly selected bath typically varies about 12.96°F from the mean of 93.2°F.

P(Sandals|Pants):

• 4/20

• 6/15

• 1/2

• 2/7

What is the probability of pulling a red marble
out of a jar of marbles that have 10 green marbles, 7 red marbles and 3 blue marbles?

• 1/7

• 7/20

• 7/10

• 3/10

What is the probability of flipping a coin twice and landing on tails both times? (leave answer in fraction form in lowest terms)

• 1/2

• 2/2

• 4/1

• 1/4

What is the probability of picking a green marble, keeping it, then picking another green marble? (leave answer in fraction form in lowest terms)

• 9/49

• 1/7

• 3/14

• 6/42

If you spin two times, what is the probability of landing on green both times? (leave answer in fraction form in lowest terms)

• 1/6

• 1/9

• 1/36

• 1/30

You roll a 6-sided number cube. What is the probability of rolling an even number three times in a row? (leave answer in fraction form in lowest terms)

• 3/100

• 1/8

• 1/6

• 1/2

A coin and a number cube with the numbers 1 through 6 are tossed. What is the probability of the coin showing tails and the number cube showing the number 3? (leave answer in fraction form in lowest terms)

• 1/12

• 1/4

• 1/8

• 1/2