AP Statistics 2017

Answers Multiple Choice Explained to Practice Test 2, Section 1

1. (D) The location of the tail indicates skew. The tail is located toward the smaller values of time,
   therefore we call this distribution skewed left (since smaller values are to the left of larger values).


2. (B) Slope, traditionally written as Δy /Δx , becomes ΔCaloriesPredicted /ΔSodium = 0.2457/1. So,
   every item with 1 additional mg. of sodium tends to have 0.2457 more calories.


3. (A) Since water and sunlight also influence plant growth, we block on those variables. Plots 1, 2, 3,
   and 4 all get more direct sunlight. Plots 5, 6, 7, and 8 all get increased water.


4. (C) The middle 80% of durations symmetrically straddles the mean of 167 minutes. That leaves 10%
   of the durations in each tail. Using Standard Normal Probabilities (Table A in the Appendix to this
   book), we find a z-score that corresponds to a 10% tail area that is ±1.28. Solving the equations
   ±1.28 = (x – 167)/76 gives us approximately 70 minutes and 264 minutes.


5. (D) Aliana’s customers were not randomly selected. But neither did she randomly assign customers to
   her treatments—she spilt her shift into three parts and applied the treatment to all customers during
   the time period.


6. (E) You can tell that the surface area estimates tend to be higher than the count estimates, but you
   cannot tell how either of them compares to the correct value.


7. (B) Measurement errors are values calculated using the expression Thermometer Reading – 20°C. If
   the reading is 18°C, then the error would be −2°C. We then need to calculate the probability that the
   error is less than −2°C. Using Table A (see Appendix), we find


8. (D) The definition of a P -value is the probability, in repeated sampling, of obtaining results at least
   as large/small as ours when the null hypothesis is actually true. Therefore, a P -value in this case says
   that there is a 7% chance of a difference at least as large if the new keyboard is no better than the old.


9. (D) Changing the largest value in a data set, in this case increasing it by two inches, would not affect
   either Q1 or Q3, therefore the IQR remains unchanged.


10. (B) The sampling distribution of the sample mean is approximately normal because n = 50 > 30.

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11. (C) The median for Hendersonville is 71 degrees. The third quartile for Sheboygan is 64 degrees.


12. (D) The 71% refers to r 2 . So r = ≈ ±0.8 Because the association is positive, r = +0.84.


13. (D) In this case 12/43 = 0.28 women were promoted and 9/24 = 0.38 men were promoted. The table
    does provide some evidence since these values are so different. It remains to be seen whether this
    difference is statistically significant.


14. (C) The values 2 and 18.5 represent Q1 and Q3 respectively. Approximately 50% of the values
    would be between Q1 and Q3.


15. (B) Point A “pulls up” on the left end of the line. Removing it would drop the left end, increasing the
    slope. Point B is pulling down near the mean value of x . Removing it would have little impact on the
    slope.