stats 107 exam 2

6. On October 19, 1987the Dow Jones Industrial Average dropped 508 points from its opening level of 2245. By what percentage did the Dow drop that day? This was the biggest one-day percentage drop ever Type the percentage in the box.

508/2245x100%=22.63%

Shape of Distribution. In a certain town, most haircuts are between $10 and $20 but a few salons cater to high-end clients and charge $30 to $60 the distribution of hair cut prices is

skewed to the left

The median of the three numbers, 1, 2 , and 15, is equal to a . I. b 2 c . 5 d. 6

b. 2

The 2008 and 2012 presidential elections. Democrat Barack Obama was elected president in 2008 and 2012. The following figure plots the percentage who voted for Obama in 2008 and 2012 for each of the 50 states and the District of Columbia. b. The correlation between these variables is r = 0.983 . What percentage of the observed variation in 2012 percentages can be explained by straight-line dependence on 2008 percentages? Type your answer in the box.

(0.983)^2=96.63%

5. Stocks go down. On February 5, 2018, the Dow Jones Industrial Average dropped 1175 points from its opening level of 25, 521 . This was the biggest one-day point decline ever. By what percentage did the Dow drop that day ? Type the percentage in the box. amount of difference/original amount x 100%= difference

1175/25,521 x 100% = 4.6%

4. Deer in the suburbs. Westchester County is a suburban area covering 438 square miles immediately north of New York City. A garden magazine claimed that the county is home to 800,000 deer. Do a calculation that shows this claim to be implausible. Type your number in the box . How does the number you calculated show that this claim is implausible?

800,000 deer/438 sq miles is roughly equivalent to 1826 deer per sq mile. number is too high to he plausible

Standard deviation Which of the following statements is true of the standard deviation? a. Removing an outlier will decrease the standard deviation. b. Removing an outlier will increase the standard deviation. c. It is the difference between the first and third quartile. d. It is the difference between the minimum and maximum values.

A. removing- decrease

A standardized reading test is given to fifth-grade students. Scores on this test are Normally distributed, with a mean of 32 points and a standard deviation of 8 points. When Corey gets his test results, he is told that his score is at the percentile. What does this mean ? a. Corey's score is higher than 95% of the students who took this test. b. Corey's score is 48 points. c. Corey's score is exactly 2 standard deviations above the mean d. All of the above .

A. 95% higher

Let's again assume that the resting pulse rates for healthy adults follow a Normal distribution with a mean of 69 beats per minute and a standard deviation of 9.5 beats per minute. When converted to a standard score, Adam's pulse rate becomes -0.5. How should this standard score be interpreted? a. Adam should see a doctor because his pulse rates is unusually low. b. Adam's pulse rate is above the mean. c. Exactly 5% of healthy adults have pulse rates less than Adam's pulse rate. d. Adam's pulse rates is about one half of a standard deviation below the mean.

D. Adams pulse rates is about one half of a standard deviation below the mean

Here are data on the percentages of words of to 15 letters used in articles in Popular Science magazine

Find the five-number summary of the distribution of word lengths from this table Min = 0.4 Q1=1.5 Median = 4.4 Q3=10.35 Max = 18.7

Where do 18- to -year-olds live? Figure stem plot of the percentage of residents aged 18 to 44 in each of the 50 states in 2010. As in Figure (253) for older residents, the stems are whole percents and the leaves are tenths of a percent. b. Describe the shape, center, and variability of this distribution . Type your answer in the box.

The distribution is roughly symmetrical centered at 35.85% and spread from 32.5% to 39.7%

Where do 18--year-olds live? Figure 11.11 a stemplot of the percentage of residents aged 18 to 44 in each of the 50 states in 2010. As in Figure 11.6 (page 253) for older residents, the stems are whole percents and the leaves are tenths of a percent. a It turns out that Utah has the largest percentage of residents aged 18 to 44 years . What is the percentage for this state? Type your answer in the box.

Utah has 39.7% young adults

The best evidence that changes in one variable cause changes in another comes from a randomized comparative experiments .b. data for which the square of the correlation is near c. higher values of the explanatory variable are associated with stronger responses .d. there is a plausible theory for causation

a . randomized comparative experiments

Extrapolation, or prediction outside the range of the data, is risky a. because the pattern observed in the data may be different outside the range of the data. b. because correlation does not necessarily imply causation. c. unless the correlation is very close to . d. unless the square of the correlation is very close to

a bc the pattern

Density curves. One characteristic of'a density curve is that there is a specific total area under the curve What is this area equal to ? a. Exactly 1 b. Approximately 1 c. it depends on what is being measured. d. It depends on whether the distribution is Normal

a. exactly 1

Suppose that resting pulse rates for healthy adults are found to follow a Normal distribution with a mean of 69 beats per minute and a standard deviation of 9.5 beats per minutes. If Bonnie has a pulse rate of 78.5 beats per minute , this means that a. Approximately 32% of adults have pulse rates higher than Bonnie's. b. Approximately 16% of adults have pulse rates higher than Bonnie's. c. Bonnie's pulse rate is two standard deviations above the mean. d. Bonnie's pulse rate, when converted to a standard score, would be 1.5.

b. approximately 16%

If the points in a scatterplot of two variables slope downward from left to right, we say the direction of the relationship between the variables is a positive. b . negative . c. strong d. weak

b. negative

Histograms. Use a histogram when a. the number of observations is small b. you want to look at the distribution of a quantitative variable. c. you want to look at the distribution of a categorical variable. d. you want to show the actual observations.d

b. you want to look at the distribution of a quantitative variable

Academic good standing. To be in good standing at college, a student needs to maintain a certain grade point average (GPA)Typically, a student who falls below 2.0 is put on academic probation for at least a semester. At a local college, administrators wanted to increase the GPA to remain in good standing from 2.0 and reported that the anticipated increase of students on probation would be from 3% to 5% of the student body. Relatively speaking, the increase in the percentage of students at the college who would be on academic probation would be 2% over the current figure b. 40\% over the current figure. c. 67% over the current figure . d We cannot determine the percentage increase because we do not know how many students attend the college .

c. 67% over the current figure

An observed relationship between two variables can be used for prediction a. as long as we know the relationship is due to direct causation. b. as long as the relationship is a straight-line relationship . c. as long as the patterns found in past data continue to hold true. d. in all of the above instances .

c. as long as the pattern found in past data continue to hold true

The five-number summary Which of the following is a graph of the five-number summary ? . A histogram b . A stemplot c A boxplot d . A bar graph

c. boxplot

When creating a scatterplot , a. always put the categorical variable on the horizontal axis. b. always put the categorical variable on the vertical axis. C. if you have an explanatory variable, put it on the horizontal axis. d. you have a response variable, put it on the horizontal axis.

c. if you have an explanatory variable

Which graph? You want to show how the price of cable television has changed over the years you should use a. pie chart b. bar graph c. line graph d side -by-side bar graph .

c. line graph

Stemplots. An advantage of a stemplot over a histogram is a. they are good for really large data sets. b. they are horizontal. c. one can recover the actual observations from the display . d. the classes are chosen for you .

c. one can recover the actual observations from the display

Shape of distributions. The following figure contains exam scores for 75 students. What is the shape of the exam score distribution? aSymmetric b. Skewed to the right c Skewed to the left d. None of the above

c. skewed to the left

The least-squares regression line a. is the line that makes the sum of the vertical distances of the data points from the line as small as possible b. is the line that makes the sum of the vertical distances of the data points from the line as large as possible c, is the line that makes the sum of the squared vertical distances of the data points from the line as small as possible d. is the line that makes the sum of the squared vertical distances of the data points from the line as large as possible

c. sum of squared vertical distances of the data points from the line as small as possible

The mean and median. Which of the following is an incorrect statement? A. If a density curve is skewed to the right, the mean will be larger than the median. b. In a symmetric density curve, the mean is equal to the median . c. The median is the balance point in a density curve. d. The mean of a skewed distribution is pulled toward the long tail.

c. the median is the balance point in a density curve

Distributions A recent report on the religious affiliation of Hispanics says 55% are Catholic, 22% Protestant, 18% unafilliated, and 4% other. This adds up to 99%. You conclude a. the remaining 1 % are not accounted for. b. there was a calculation or data entry error c this is due to roundoff error d there is a religion missing from the survey .

c. this is due to roundoff error

3. Classes on Fridays. A professor is concerned that not enough courses at his college hold class meetings on FridaysAfter speaking with administrators, the professor finds out that 15\% of courses have class meetings on Fridays. At this school, classes meet on either Monday-Wednesday-Friday or Tuesday-Thursday and do not meet on Saturday or Sunday a. The 15% figure is about right because Friday is one of seven days of the week. b. The 15% figure is low because it is less than 20%, and Friday is one of five days on which classes meet . c. We cannot make a decision about the 15% figure because we do not know how courses are divided among teaching days (e.g.Monday-Wednesday-Friday or Tuesday-Thursday). D. The 15\% figure is high because students tend to skip classes on Fridays.

c. we cannot make a decision

Mean The mean of the three numbers, 1, 2 , and 15, is equal to a . I b 2 c . 5 d. 6

d. 6

which of the following is true of the correlation r? a. cant be greater than 1 or less than -1 b. measures the strength of the straight line btw 2 quantitative variables c. correlation of +1 or -1 only happen if there is a perfect straight line btw 2 quant variables d. all

d. all of the above

7. Categorical and quantitative variables A survey was conducted and respondents were asked what color car they drive and how many miles they travel per day. The variable type for "car color" and "miles per day" are a. both categorical b. both quantitative c. car color is quantitative , miles per day is categorical d. car color is categorical , miles per day is quantitative

d. car color is categorical miles per day is quantitative

2. Decreasing household trash. A large city has started a new recycling program that aims to reduce household trash by 25% by educating residents about more household items that can be recycled. A friend of yours says, This is great! The amount of recycling will increase by 25%. That's a great start!" What is wrong with your friend's comment? Your friend assumed that the amount of trash and the amount of recycling was equal to begin with. b. We know that a 25% reduction in household trash will result in less than a 25\% increase in recycling. We know that a 25 % reduction in household trash will result in more than a 25% increase in recycling. d. None of the above.

d. none of the above

The quantity that tells us what fraction of the variation in the responses is explained by the straight-line tie between the response and explanatory variables is a. the correlation . b. the absolute value of the correlation. c. the square root of the correlation. d. the square of the correlation.

d. the square of the correlation

The 2008 and 2012 presidential elections. Democrat Barack Obama was elected president in 2008 and 2012. The following figure plots the percentage who voted for Obama in 2008 and 2012 for each of the 50 states and the District of Columbia . a Describe in words the direction, formand strength of the relationship between the percentage of votes for Obama in 2008 and the percentage in 2012. Type your answer in the box.

direction- pos form- linear strength- strong