Probability and Statistics — Answer Key
Part A: Fill in the Blank
Write the missing word or number on each line.
1. When you flip 2 fair coins, the total number of equally likely outcomes is 4.
2 outcomes for the first coin times 2 for the second equals 4 total.
2. P(both heads) when flipping 2 coins = 1/4.
One favorable outcome (HH) out of 4 equally likely outcomes is 1/4.
3. A tree diagram for flipping 2 coins has 4 branches at the second level total.
2 first-level branches each split into 2, giving 2 x 2 = 4 endpoints.
4. In the set 4, 5, 6, 7, 80, the value 80 is an outlier.
80 is much larger than the other values 4 through 7, making it the outlier.
5. Removing the outlier 80 from 4, 5, 6, 7, 80 will most affect the mean (mean/median).
The mean depends on all values, so a far value pulls it strongly; the median barely moves.
6. P(getting tails then heads) on 2 coin flips = 1/4.
One favorable ordered outcome out of 4 equally likely outcomes is 1/4.
7. P(at least one head) on 2 coin flips = 3/4.
Three of four outcomes contain at least one head, so P = 3/4.
8. A bar graph is best for comparing totals across categories.
Bar graphs show category totals so you can compare amounts at a glance.
9. A line plot is best for showing the frequency of repeated measurements.
Line plots use Xs or dots to show how frequently each value appears in the data.
Part B: Matching
Match each item on the left to the correct answer on the right.
1. Match each item to its correct answer.
P(HH) on 2 coins
→ 1/4
1/4
Outlier in 2,3,4,50
→ 50
50
Best display: items per category
→ Bar graph
Bar graph
Best display: frequency of values
→ Line plot
Line plot
P(HH) is 1/4; 50 is far from 2,3,4 so it is the outlier; bars compare categories; line plots show frequency.