Arithmetic operators in Ruby - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the + operator do in Ruby?

The + operator adds two numbers together. For example, 2 + 3 equals 5.

beginner

How do you perform division in Ruby and what is the result type?

Use the / operator to divide numbers. If both numbers are integers, Ruby returns an integer (floor division). To get a float result, use at least one float number, e.g., 5.0 / 2 returns 2.5.

beginner

What is the difference between * and ** in Ruby?

* multiplies two numbers, while ** raises a number to the power of another. For example, 3 * 4 is 12, but 3 ** 4 is 81 (3 to the power of 4).

beginner

What does the % operator do in Ruby?

The % operator gives the remainder of division between two numbers. For example, 7 % 3 equals 1 because 7 divided by 3 leaves a remainder of 1.

intermediate

How can you combine arithmetic operators in Ruby?

You can combine operators like +, -, *, /, and % in expressions. Ruby follows standard math order: parentheses first, then exponentiation, multiplication/division/modulus, and finally addition/subtraction.

What is the result of 10 / 4 in Ruby if both are integers?

A 3

B 2.5

C 4

D 2

When dividing two integers, Ruby returns the integer part only (floor division), so 10 / 4 equals 2.

Which operator raises a number to a power in Ruby?

A **

B *

C +

D %

The ** operator is used for exponentiation in Ruby.

What does 15 % 4 return?

A 1

B 3

C 11

D 4

The modulus operator % returns the remainder. 15 divided by 4 leaves remainder 3.

Which operator has the highest precedence in Ruby arithmetic?

A **

B *

C +

D -

Exponentiation ** has higher precedence than multiplication, division, addition, and subtraction.

What is the result of 2 + 3 * 4 in Ruby?

A 20

B 24

C 14

D 10

Multiplication happens before addition, so 3 * 4 = 12, then 2 + 12 = 14.

Explain how Ruby handles division between two integers and how to get a decimal result.

Think about how dividing 5 by 2 behaves differently with integers and floats.

Describe the order of operations for arithmetic operators in Ruby.

Remember the math rule PEMDAS but adapted for Ruby operators.

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