Arithmetic operators in Ruby - Mini Project: Build & Apply

Arithmetic operators

📖 Scenario: You are helping a small shop owner calculate prices and discounts for products.

🎯 Goal: Build a simple Ruby program that uses arithmetic operators to calculate total price, discount, and final price.

📋 What You'll Learn

Create variables with exact values for product price and quantity

Create a variable for discount rate

Calculate total price and discount amount using arithmetic operators

Print the final price after discount

💡 Why This Matters

🌍 Real World

Calculating prices and discounts is common in shops and online stores.

💼 Career

Understanding arithmetic operators is essential for programming tasks involving calculations.

1

Create initial product data

Create a variable called price and set it to 50. Create a variable called quantity and set it to 3.

Ruby

# Create variables price and quantity with given values
# Your code here

Hint

Use = to assign values to variables.

2

Add discount rate

Create a variable called discount_rate and set it to 0.1 (which means 10%).

Ruby

price = 50
quantity = 3
# Create variable discount_rate with value 0.1
# Your code here

Hint

Discount rate is a decimal number representing percentage.

3

Calculate total price and discount

Create a variable called total_price that multiplies price and quantity. Create a variable called discount_amount that multiplies total_price and discount_rate.

Ruby

price = 50
quantity = 3
discount_rate = 0.1
# Calculate total_price and discount_amount
# Your code here

Hint

Use * for multiplication.

4

Print final price after discount

Create a variable called final_price that subtracts discount_amount from total_price. Then print final_price using puts.

Ruby

price = 50
quantity = 3
discount_rate = 0.1
total_price = price * quantity
discount_amount = total_price * discount_rate
# Calculate final_price and print it
# Your code here

Hint

Use - to subtract and puts to print.

Practice

1. Which of the following is the correct symbol for multiplication in Ruby?

easy

A. -

B. *

C. +

D. /

Solution

1. Step 1: Recall basic arithmetic symbols in Ruby

   Ruby uses standard arithmetic symbols: + for addition, - for subtraction, * for multiplication, / for division.

2. Step 2: Identify the multiplication symbol

   The symbol for multiplication is the asterisk (*).

3. Final Answer:

   * -> Option B

4. Quick Check:

   Multiplication = * [OK]

Hint: Remember * means multiply in most languages including Ruby [OK]

Common Mistakes:

• Confusing + with multiplication
• Using / instead of *
• Using - instead of *

2. Which of the following Ruby expressions correctly calculates the remainder of 10 divided by 3?

easy

A. 10 - 3

B. 10 / 3

C. 10 * 3

D. 10 % 3

Solution

1. Step 1: Understand the modulus operator

   The modulus operator (%) returns the remainder after division.

2. Step 2: Identify the correct expression for remainder

   10 % 3 calculates the remainder when 10 is divided by 3, which is 1.

3. Final Answer:

   10 % 3 -> Option D

4. Quick Check:

   Remainder = % [OK]

Hint: Use % to get remainder after division [OK]

Common Mistakes:

• Using / instead of %
• Using * or - which do not give remainder
• Confusing % with division

3. What is the output of the following Ruby code?

result = 15 / 4
puts result

medium

A. 3

B. SyntaxError

C. 4

D. 3.75

Solution

1. Step 1: Understand integer division in Ruby

   When dividing two integers, Ruby performs integer division, discarding the decimal part.

2. Step 2: Calculate 15 divided by 4 as integer division

   15 / 4 equals 3.75, but integer division returns 3.

3. Final Answer:

   3 -> Option A

4. Quick Check:

   Integer division truncates decimals = 3 [OK]

Hint: Integer division drops decimals unless floats used [OK]

Common Mistakes:

• Expecting float result without floats
• Confusing / with %
• Thinking output is 4 or 3.75

4. Identify the error in this Ruby code snippet:

num = 10
result = num / 0
puts result

medium

A. Division by zero error

B. Syntax error due to missing operator

C. No error, output is 0

D. Variable 'num' is undefined

Solution

1. Step 1: Analyze the division operation

   The code divides 10 by 0, which is mathematically undefined.

2. Step 2: Understand Ruby's behavior on division by zero

   Ruby raises a ZeroDivisionError when dividing by zero.

3. Final Answer:

   Division by zero error -> Option A

4. Quick Check:

   Dividing by zero causes error [OK]

Hint: Never divide by zero; it causes runtime error [OK]

Common Mistakes:

• Thinking output is 0
• Assuming syntax error
• Ignoring runtime exceptions

5. You want to calculate the average of three numbers: 7, 8, and 9 in Ruby. Which expression correctly computes the average as a float?

hard

A. 7 + 8 + 9 / 3

B. (7 + 8 + 9) / 3

C. (7 + 8 + 9) / 3.0

D. (7 + 8 + 9) % 3

Solution

1. Step 1: Calculate sum of numbers

   Sum is 7 + 8 + 9 = 24.

2. Step 2: Divide by 3 as float division

   Dividing by 3.0 forces float division, giving 8.0 instead of integer 8.

3. Final Answer:

   (7 + 8 + 9) / 3.0 -> Option C

4. Quick Check:

   Use float divisor for float average [OK]

Hint: Divide by float (3.0) to get decimal average [OK]

Common Mistakes:

• Using integer division losing decimals
• Misusing % instead of /
• Wrong operator precedence without parentheses