Why statistical tools drive decisions in MATLAB - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to calculate the mean of the data array.

MATLAB

data = [5, 10, 15, 20, 25];
meanValue = [1](data);

Drag options to blanks, or click blank then click option'

Asum

Bmedian

Cmean

Dmode

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'sum' instead of 'mean' will give the total, not the average.

Using 'median' or 'mode' calculates different statistical measures.

The mean function calculates the average value of the data array, which is essential for understanding the central tendency in statistics.

2fill in blank

medium

Complete the code to calculate the standard deviation of the data array.

MATLAB

data = [5, 10, 15, 20, 25];
stdDev = [1](data);

Drag options to blanks, or click blank then click option'

Astd

Bvar

Cmean

Dsum

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'var' calculates variance, not standard deviation.

Using 'mean' or 'sum' does not measure spread.

The std function calculates the standard deviation, which measures how spread out the data values are from the mean.

3fill in blank

hard

Fix the error in the code to calculate the median of the data array.

MATLAB

data = [5, 10, 15, 20, 25];
medianValue = [1](data);

Drag options to blanks, or click blank then click option'

Amean

Bmedian

Cmed

Dmode

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'med' instead of 'median' causes a function not found error.

Using 'mean' calculates average, not median.

The correct function to calculate the median in MATLAB is median. Using 'med' will cause an error because it is not a valid function.

4fill in blank

hard

Fill both blanks to create a dictionary (struct) of word lengths for words longer than 3 characters.

MATLAB

words = {'data', 'is', 'fun', 'and', 'useful'};
lengths = struct();
for i = 1:length(words)
    word = words{i};
    if length(word) [1] 3
        lengths.([2]) = length(word);
    end
end

Drag options to blanks, or click blank then click option'

A>

B<

Cword

Dlength

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' instead of '>' will select shorter words.

Using 'length' as a field name causes errors because it's a function.

The condition length(word) > 3 checks for words longer than 3 characters. Using word as the field name in the struct stores the length keyed by the word itself.

5fill in blank

hard

Fill all three blanks to create a struct of word lengths for words with length greater than 3.

MATLAB

words = {'apple', 'cat', 'banana', 'dog'};
lengths = struct();
for i = 1:length(words)
    word = words{i};
    if length(word) [1] 3
        lengths.([2]) = [3](word);
    end
end

Drag options to blanks, or click blank then click option'

A>

Bword

Clength

Dnumel

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' instead of '>' in the condition.

Using 'numel' instead of 'length' for strings may work but is less common.

Using a wrong field name causes errors.

The condition length(word) > 3 selects words longer than 3 characters. The struct field is named by the word itself, and length(word) gives the number of characters.

Practice

1. Why do we use statistical tools like mean and std in MATLAB when making decisions?

easy

A. To make the code run faster

B. To change the data values randomly

C. To understand data patterns and make informed decisions

D. To create graphics only

Solution

1. Step 1: Understand the purpose of statistical tools

   Statistical tools like mean and standard deviation help summarize data and show patterns.

2. Step 2: Connect tools to decision making

   By understanding data patterns, we can make better, informed decisions rather than guessing.

3. Final Answer:

   To understand data patterns and make informed decisions -> Option C

4. Quick Check:

   Statistical tools guide decisions = B [OK]

Hint: Statistical tools summarize data to guide decisions [OK]

Common Mistakes:

• Thinking statistical tools speed up code
• Believing they randomly change data
• Assuming they only create graphics

2. Which MATLAB command correctly calculates the average of the vector A = [4, 8, 12]?

easy

A. average(A)

B. mean(A)

C. sum(A)

D. std(A)

Solution

1. Step 1: Identify the function for average in MATLAB

   The function mean() calculates the average of numbers in a vector.

2. Step 2: Check other options

   average() is not a MATLAB function, sum() adds values, and std() calculates standard deviation.

3. Final Answer:

   mean(A) -> Option B

4. Quick Check:

   Average = mean() [OK]

Hint: Use mean() to find average in MATLAB [OK]

Common Mistakes:

• Using average() which is not a MATLAB function
• Confusing sum() with average
• Using std() instead of mean()

3. What is the output of this MATLAB code?

A = [2, 4, 6, 8];
m = mean(A);
s = std(A);
disp([m, s]);

medium

A. [5 2.58199]

B. [4 2]

C. [6 3]

D. [5 3]

Solution

1. Step 1: Calculate the mean of A

   Mean = (2 + 4 + 6 + 8) / 4 = 20 / 4 = 5.

2. Step 2: Calculate the standard deviation of A

   Standard deviation ≈ 2.58199 for these values.

3. Final Answer:

   [5 2.58199] -> Option A

4. Quick Check:

   mean = 5, std ≈ 2.58 [OK]

Hint: Calculate mean and std separately, then display [OK]

Common Mistakes:

• Mixing up mean and std values
• Calculating sum instead of mean
• Using wrong formula for std

4. Find the error in this MATLAB code that tries to calculate the mean of B = [1, 3, 5, 7]:

B = [1, 3, 5, 7];
average = mean(B);
disp(average);

medium

A. mean() function is not defined in MATLAB

B. Missing semicolon after mean(B)

C. disp() cannot display variables

D. Variable name 'average' overwrites a function

Solution

1. Step 1: Check variable naming

   Using 'average' as a variable name is allowed but can confuse readers since it looks like a function name.

2. Step 2: Confirm syntax correctness

   There is no syntax error; semicolon is optional for suppressing output, mean() is a valid function, and disp() can display variables.

3. Final Answer:

   Variable name 'average' overwrites a function -> Option D

4. Quick Check:

   Variable name shadows function = C [OK]

Hint: Avoid naming variables same as functions [OK]

Common Mistakes:

• Thinking semicolon is mandatory
• Believing mean() is undefined
• Assuming disp() can't show variables

5. You have two data sets in MATLAB:

data1 = [10, 20, 30, 40];
data2 = [15, 25, 35, 45];

Which statistical tool helps decide if the difference between these sets is significant for decision making?

hard

A. t-test

B. std

C. sum

D. mean

Solution

1. Step 1: Understand the goal

   We want to check if the difference between two data sets is statistically significant.

2. Step 2: Identify the correct statistical test

   Mean and std show averages and spread but do not test significance. The t-test compares means to check significance.

3. Final Answer:

   t-test -> Option A

4. Quick Check:

   Significance test = t-test [OK]

Hint: Use t-test to compare two data sets statistically [OK]

Common Mistakes:

• Using mean or std to test significance
• Confusing sum with statistical tests
• Ignoring the need for a significance test