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This quiz was administered in-person. It was closed-book and
closed-note; students **were not** allowed to use the DSC
10 Reference Sheet. Students had **20 minutes** to work on
the quiz.

This quiz covered Lectures 14-17 of the Fall 2023 offering of
DSC 10.

Ciro is an avid fan of Costco, a members-only warehouse store. On his recent trip to the Morena Boulevard location near campus, he was surprised by how full shoppers’ carts were and was inspired to investigate how much people typically spend at Costco.

Among all Costco members in San Diego, the average monthly spending
in October 2023 was **$350** with a standard deviation of
**$40**.

The amount Ciro spent at Costco in October 2023 was
**-1.5** in standard units. What is this amount in dollars?
Give your answer as an integer.

**Answer**: 290

The average score on this problem was 93%.

What is the minimum possible percentage of San Diego members that
spent between **$250** and **$450** in October
2023?

16%

22%

36%

60%

78%

84%

**Answer**: 84%

The average score on this problem was 61%.

Now, suppose we’re given that the distribution of monthly spending in October 2023 for all San Diego members is roughly normal. Given this fact, fill in the blanks:

What are m and n? Give your answers as integers rounded to the nearest multiple of 10.

**Answer**: m: 270, n: 430

The average score on this problem was 81%.

Suppose we have access to a simple random sample of all US Costco
members of size **145**. Our sample is stored in a
DataFrame named `us_sample`

, in which the
`"Spend"`

column contains the October 2023 spending of each
sampled member in dollars.

Fill in the blanks:

`"Spend"`

column in `us_sample`

is a ____,
while the average October 2023 spending of all US members is a ____."
sample statistic; population parameter

population statistic; sample parameter

sample parameter; population statistic

population parameter; sample statistic

**Answer**: sample statistic; population parameter

The average score on this problem was 94%.

Fill in the blanks below so that `us_left`

and
`us_right`

are the left and right endpoints of a
**46%** confidence interval for the average October 2023
spending of all US members.

```
= np.array([])
costco_means for i in np.arange(5000):
= __(x)__
resampled_spends = np.append(costco_means, resampled_spends.mean())
costco_means = np.percentile(costco_means, __(y)__)
left = np.percentile(costco_means, __(z)__) right
```

Which of the following could go in blank (x)? **Select all that
apply.**

`us_sample.sample(145, replace=True).get("Spend")`

`us_sample.sample(145, replace=False).get("Spend")`

`np.random.choice(us_sample.get("Spend"), 145)`

`np.random.choice(us_sample.get("Spend"), 145, replace=True)`

`np.random.choice(us_sample.get("Spend"), 145, replace=False)`

None of the above.

What goes in blanks (y) and (z)? Give your answers as integers.

**Answer**:

`x`

:`us_sample.sample(145, replace=True).get("Spend")`

`np.random.choice(us_sample.get("Spend"), 145)`

`np.random.choice(us_sample.get("Spend"), 145, replace=True)`

`y`

:`27`

`z`

:`73`

The average score on this problem was 79%.

True or False: **46%** of all US members in
`us_sample`

spent between `us_left`

and
`us_right`

in October 2023.

True

False

**Answer**: False

The average score on this problem was 85%.

True or False: If we repeat the code from part (b) 200 times, each
time bootstrapping from a new random sample of 145 members drawn from
all US members, then about **92** of the intervals we
create will contain the average October 2023 spending of all US
members.

True

False

**Answer**: True

The average score on this problem was 51%.

True or False: If we repeat the code from part (b) 200 times, each
time bootstrapping from `us_sample`

, then about
**92** of the intervals we create will contain the average
October 2023 spending of all US members.

True

False

**Answer**: False

The average score on this problem was 30%.