Part 2 — Answer key

Compare your answers after you have finished Part 1.

1. Before blowing out birthday candles, what do people traditionally do first?
   Make a wish silently
2. The melody of "Happy Birthday to You" was originally published as a classroom song called "Good Morning to All."
   True
3. In Western astrology, your zodiac sign is determined primarily by your what?
   Birth date (month and day)
4. In the Gregorian calendar, every year divisible by 4 is a leap year.
   False
5. A "golden birthday" usually means you turn the age that matches what?
   The day of the month you were born
6. As of 2023 in the United States, you can vote in federal elections at age 18.
   True
7. What is the traditional birthstone for April?
   Diamond
8. In many hospitals, which day of the week tends to have fewer births because fewer planned inductions and C-sections are scheduled?
   Sunday
9. Over the long run in the Gregorian calendar, roughly 1 out of every 1,461 days is Feb 29.
   True
10. Before it became the standard birthday song, the same melody was best known with which opening line?
    Good morning to all
11. In Hebrew, the word "mitzvah" most literally means what?
    Commandment
12. In U.S. birth data, major holidays like Christmas often show a noticeable dip in births compared with nearby non-holiday dates.
    True
13. In the United States, the age most associated with Medicare eligibility is what?
    65
14. A person born on Feb 29 is sometimes nicknamed a what?
    Leapling
15. In traditional practice, a bat mitzvah is often associated with reaching about what age?
    12
16. You see a post claiming “September 9 is the most common birthday.” Which missing detail matters most before you decide whether that claim is meaningful?
    The country and years of the data
17. Assuming birthdays are evenly spread across 365 days and ignoring Feb 29, a group of 23 people has a greater than 50% chance that two share a birthday.
    True
18. Under the classic birthday paradox assumptions (uniform across 365 days), about how many people are needed for the chance of a shared birthday to exceed 99%?
    57
19. You are in a group of 30 people. Using the classic birthday paradox assumptions, which is closest to the chance that at least two people share a birthday?
    About 70%
20. Ignoring Feb 29, if 366 people are in a room, at least two must share the same birthday.
    True
21. Which of these years is a leap year under the Gregorian rules?
    2000
22. Someone born on Feb 29 legally "ages" only once every four years.
    False
23. You move to Japan and turn 18. Which statement best matches the national rules after Japan lowered the age of majority?
    You can sign many contracts but still cannot buy alcohol
24. In the United States, the minimum age to be elected President is what?
    35
25. In the United States, it is legal everywhere for an 18-year-old to buy alcohol as long as a parent is present.
    False
26. Looking at daily birth totals in many places, which date often stands out as unusually low because it is both a major holiday and a common day for avoiding scheduled deliveries?
    Dec 25
27. Which pattern is most commonly observed in modern hospital birth data?
    More births on weekdays than weekends
28. You are comparing which month is "most common for birthdays" using monthly totals. What is the fairest quick adjustment so February does not look artificially low just because it has fewer days?
    Use births per day
29. Because February is the shortest month, it is automatically the rarest birth month in every country and every dataset.
    False
30. People are shocked by the birthday paradox mainly because they underestimate what?
    How many possible pairs exist in a group
31. Over a full 400-year Gregorian cycle, how many leap days occur?
    97
32. A key reason bat mitzvah ceremonies became more widespread in the modern era is what?
    Expanded Jewish education and participation for girls
33. A bar or bat mitzvah is a status reached by age, it does not require a rabbi or a specific ceremony to make it valid.
    True
34. Which statement about bar mitzvah and bat mitzvah is most accurate across Jewish communities?
    Bar at 13 and bat at 12 are traditional ages, but timing and rituals vary by community
35. You collect birthdays from 50 random people and assume birthdays are uniformly distributed across 365 days (ignore Feb 29). What is the expected number of matching pairs of people who share a birthday, counting each matching pair once?
    About 3.4
36. In "bar mitzvah," the word "bar" comes from Aramaic and most literally means what?
    Son