Arithmetic operators in Ruby - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of mixed arithmetic operations

What is the output of this Ruby code?

Ruby

result = 10 + 5 * 2 - 8 / 4
puts result

A 24

B 18

C 14

D 12

💡 Hint

Remember the order of operations: multiplication and division happen before addition and subtraction.

Multiplication and division are done first: 5 * 2 = 10, 8 / 4 = 2. Then addition and subtraction: 10 + 10 - 2 = 18. But wait, check carefully: 10 + (5*2) - (8/4) = 10 + 10 - 2 = 18. So correct output is 18.

❓ Predict Output

intermediate

Integer division vs float division

What will this Ruby code print?

Ruby

a = 7 / 2
b = 7 / 2.0
puts a
puts b

A

3.5
3

B

3
3

C

3
3.5

D

3.5
3.5

💡 Hint

Division with integers truncates the decimal part, but with floats it keeps it.

7 / 2 is integer division, so result is 3. 7 / 2.0 involves a float, so result is 3.5.

🔧 Debug

advanced

Identify the error in arithmetic expression

What error does this Ruby code raise?

Ruby

x = 5 + * 3
puts x

A SyntaxError

B TypeError

C NoMethodError

D ZeroDivisionError

💡 Hint

Look carefully at the operator usage between numbers.

The expression '5 + * 3' is invalid syntax because two operators '+' and '*' are adjacent without a number between them.

❓ Predict Output

advanced

Modulo operator behavior

What is the output of this Ruby code?

Ruby

puts -13 % 5

A 2

B -3

C -2

D 3

💡 Hint

Modulo in Ruby always returns a non-negative remainder when the divisor is positive.

In Ruby, -13 % 5 returns 2 because it finds the remainder that makes the result non-negative.

🧠 Conceptual

expert

Result of chained assignment with arithmetic

What is the value of variable 'a' after running this Ruby code?

Ruby

a = b = 10
b += 5
c = a + b

A 5

B 15

C 25

D 10

💡 Hint

Remember that 'a' and 'b' are assigned independently and changing 'b' after does not affect 'a'.

Initially, both 'a' and 'b' are 10. Then 'b' is increased by 5 to 15. 'a' remains 10. So 'a' is 10 after all operations.

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