Chapter 6: Q. 6.6 (page 435)
Orange M&M鈥橲
a. Find and interpret the expected value of .
b. Find and interpret the standard deviation of .
Short Answer
- The required Expected value of candies.
- The required Standard deviation of X, candies
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Chapter 6: Q. 6.6 (page 435)
Orange M&M鈥橲
a. Find and interpret the expected value of .
b. Find and interpret the standard deviation of .
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Quick, click! An Internet reaction time test asks subjects to click their mouse button as soon as a light flashes on the screen. The light is programmed to go on at a randomly selected time after the subject clicks 鈥淪tart.鈥 The density curve models the amount of time Y (in seconds) that the subject has to wait for the light to flash.
a) Find and interpret
b) What is ? Explain your answer.
c) Find the value of k that makes this statement true:

Get on the boat! A small ferry runs every half hour from one side of a large river to the other. The probability distribution for the random variable Y = money collected (in dollars) on a randomly selected ferry trip is shown here.

Part (a). Find . Interpret this result.
Part (b). Express the event 鈥渁t least $20 is collected鈥 in terms of Y. What is the probability of this event?
Working outExercise 10 described a large sample survey that asked a sample of people aged 19 to 25 years, 鈥淚n the past seven days, how many times did you go to an exercise or fitness center or work out?鈥 The response Y for a randomly selected survey respondent has the probability distribution shown here. From Exercise 10, . Find the standard deviation of Y. Interpret this value.

.Essay errors Typographical and spelling errors can be either 鈥渘onword errors鈥 or 鈥渨ord errors.鈥 A nonword error is not a real word, as when 鈥渢he鈥 is typed as 鈥渢eh.鈥 A word error is a real word, but not the right word, as when 鈥渓ose鈥 is typed as 鈥渓oose.鈥 When students are asked to write a -word essay (without spell-checking), the number of nonword errors X has the following probability distribution:
| Value of X | 0 | 1 | 2 | 3 | 4 |
| Probability | 0.1 | 0.2 | 0.3 | 0.3 | 0.1 |
| Value of Y | 0 | 1 | 2 | 3 |
| Probability | 0.4 | 0.3 | 0.2 | 0.1 |
a) Find the mean and standard deviation of the difference in the number of errors made by a randomly selected student. Interpret each value in context.
(b) Challenge: Find the probability that a randomly selected student makes more word errors than nonword errors .
Spoofing (4.2) To collect information such as passwords, online criminals use "spoofing" to direct Internet users to fraudulent websites. In one study of Internet fraud, students were warned about spoofing and then asked to log into their university account starting from the university's home page. In some cases, the log-in link led to the genuine dialog box. In others, the box looked genuine but, in fact, was linked to a different site that recorded the ID and password the student entered. The box that appeared for each student was determined at random. An alert student could detect the fraud by looking at the true Internet address displayed in the browser status bar, but most just entered their ID and password.
a. Is this an observational study or an experiment? Justify your answer.
b. What are the explanatory and response variables? Identify each variable as categorical or quantitative.
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