Descriptive statistics review in Data Analysis Python - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Calculate mean and median from a list

What is the output of the following code that calculates the mean and median of a list of numbers?

Data Analysis Python

import statistics
numbers = [10, 20, 30, 40, 50]
mean_val = statistics.mean(numbers)
median_val = statistics.median(numbers)
print(mean_val, median_val)

A 30 25

B 30 20

C 25 30

D 30.0 30.0

💡 Hint

Mean is the average, median is the middle value when sorted.

The mean is the sum of all numbers divided by count: (10+20+30+40+50)/5 = 30. The median is the middle number in sorted order, which is 30.

❓ data_output

intermediate

Count unique values in a DataFrame column

Given a DataFrame with a column of colors, what is the output of counting unique values in that column?

Data Analysis Python

import pandas as pd
data = {'color': ['red', 'blue', 'red', 'green', 'blue', 'blue']}
df = pd.DataFrame(data)
unique_counts = df['color'].value_counts()
print(unique_counts)

A

green   3
red     2
blue    1
Name: color, dtype: int64

B

red     3
blue    2
green   1
Name: color, dtype: int64

C

blue    3
red     2
green   1
Name: color, dtype: int64

D

blue    2
red     2
green   2
Name: color, dtype: int64

💡 Hint

Count how many times each color appears.

The color 'blue' appears 3 times, 'red' 2 times, and 'green' once. value_counts() sorts by count descending by default.

❓ visualization

advanced

Identify the correct boxplot visualization

Which option shows the correct boxplot for the data [5, 7, 8, 12, 15, 18, 22]?

Data Analysis Python

import matplotlib.pyplot as plt
data = [5, 7, 8, 12, 15, 18, 22]
plt.boxplot(data)
plt.show()

A Boxplot with median line near 8, whiskers from 5 to 15, no outliers

B Boxplot with median line near 12, whiskers from 5 to 22, no outliers

C Boxplot with median line near 15, whiskers from 7 to 18, outliers at 5 and 22

D Boxplot with median line near 12, whiskers from 7 to 22, outlier at 5

💡 Hint

Median is the middle value; whiskers cover min and max if no outliers.

The median of the data is 12. The minimum is 5 and maximum is 22. No values are far enough to be outliers, so whiskers span min to max.

🧠 Conceptual

advanced

Understanding standard deviation effect

If two datasets have the same mean but one has a larger standard deviation, what does this mean about the data?

A The dataset with larger standard deviation has values more spread out from the mean

B The dataset with larger standard deviation has values closer to the mean

C Both datasets have identical value distributions

D Standard deviation does not relate to data spread

💡 Hint

Think about how spread out the numbers are around the average.

Standard deviation measures how much values differ from the mean. Larger standard deviation means more spread out values.

🔧 Debug

expert

Identify the error in variance calculation code

What error does the following code raise when calculating variance of a list?

Data Analysis Python

data = [4, 8, 15, 16, 23, 42]
variance = sum((x - sum(data)/len(data))**2 for x in data) / (len(data) - 1)
print(variance)

A No error, prints correct variance value

B ZeroDivisionError because len(data) - 1 is zero

C TypeError because sum() is used incorrectly

D NameError because variable 'variance' is not defined

💡 Hint

Check if denominator is zero and if sum() is used correctly.

The code correctly calculates sample variance using the formula. len(data) is 6, so denominator is 5, no division by zero. sum() is used correctly.