Operator precedence in Javascript - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to correctly add 2 and 3, then multiply by 4.

Javascript

let result = (2 + 3) [1] 4;
console.log(result);

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

A*

B+

C-

D/

Attempts:

3 left

💡 Hint

Common Mistakes

Using + instead of * causes the result to be 5 + 4 = 9, which is incorrect.

Using - or / changes the meaning and result unexpectedly.

Multiplication (*) has higher precedence than addition (+), so (2 + 3) * 4 equals 20.

2fill in blank

medium

Complete the code to get the correct result of 2 + 3 * 4 without parentheses.

Javascript

let result = 2 + 3 [1] 4;
console.log(result);

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

A+

B/

C-

D*

Attempts:

3 left

💡 Hint

Common Mistakes

Using + instead of * causes the operations to be done left to right, which is not correct here.

Using - or / changes the calculation and result.

Multiplication (*) has higher precedence than addition (+), so 3 * 4 is done first, then 2 is added, resulting in 14.

3fill in blank

hard

Fix the error in the expression to get the correct result of 10 minus 2 times 3.

Javascript

let result = 10 [1] 2 * 3;
console.log(result);

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

A*

B-

C+

D/

Attempts:

3 left

💡 Hint

Common Mistakes

Using + instead of - changes the result to 16.

Using * or / here changes the meaning and causes wrong results.

Subtraction (-) is needed to get 10 - 2 * 3. Multiplication happens first, so 2 * 3 = 6, then 10 - 6 = 4.

4fill in blank

hard

Fill both blanks to create an expression that divides 20 by 5 and then adds 3.

Javascript

let result = 20 [1] 5 [2] 3;
console.log(result);

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

A/

B+

C-

D*

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping the operators changes the result.

Using subtraction or multiplication instead of addition changes the meaning.

Division (/) happens before addition (+), so 20 / 5 = 4, then 4 + 3 = 7.

5fill in blank

hard

Fill all three blanks to create an expression that multiplies 4 by 3, subtracts 2, then adds 5.

Javascript

let result = 4 [1] 3 [2] 2 [3] 5;
console.log(result);

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

A*

B-

C+

D/

Attempts:

3 left

💡 Hint

Common Mistakes

Changing the order of operators changes the result.

Using division instead of multiplication changes the meaning.

Multiplication (*) happens first: 4 * 3 = 12, then subtraction (-) 12 - 2 = 10, then addition (+) 10 + 5 = 15.

Practice

1. Which operator has the highest precedence in the expression 3 + 4 * 2?

easy

A. Multiplication (*)

B. Addition (+)

C. Subtraction (-)

D. Division (/)

Solution

1. Step 1: Recall operator precedence rules

   Multiplication and division have higher precedence than addition and subtraction.

2. Step 2: Identify operators in the expression

   The expression has addition (+) and multiplication (*). Multiplication runs first.

3. Final Answer:

   Multiplication (*) -> Option A

4. Quick Check:

   Multiplication > Addition [OK]

Hint: Multiplication/division run before addition/subtraction [OK]

Common Mistakes:

• Thinking addition runs before multiplication
• Ignoring operator precedence
• Assuming left-to-right always applies

2. Which of the following expressions is syntactically correct in JavaScript?

easy

A. 5 + (3 * 2)

B. 5 + * 3

C. 5 + 3 * )2(

D. 5 + 3 * 2)

Solution

1. Step 1: Check each expression for syntax errors

   5 + * 3 has two operators in a row (+ *), which is invalid. 5 + 3 * )2( has misplaced parentheses. 5 + 3 * 2) has an unmatched closing parenthesis.

2. Step 2: Confirm correct syntax

   5 + (3 * 2) uses parentheses correctly and has valid operators and operands.

3. Final Answer:

   5 + (3 * 2) -> Option A

4. Quick Check:

   Valid parentheses and operators [OK]

Hint: Check parentheses and operator placement carefully [OK]

Common Mistakes:

• Misplacing parentheses
• Using two operators together
• Unmatched parentheses

3. What is the output of the following code?

console.log(10 - 2 * 3 + 4 / 2);

medium

A. 8

B. 12

C. 6

D. 10

Solution

1. Step 1: Apply operator precedence

   Multiplication (*) and division (/) run before addition (+) and subtraction (-). Calculate 2 * 3 = 6 and 4 / 2 = 2 first.

2. Step 2: Calculate remaining expression

   Expression becomes 10 - 6 + 2. Calculate left to right: 10 - 6 = 4, then 4 + 2 = 6.

3. Final Answer:

   6 -> Option C

4. Quick Check:

   10 - 6 + 2 = 6 [OK]

Hint: Do * and / before + and -, then left to right [OK]

Common Mistakes:

• Adding before multiplying
• Ignoring division precedence
• Calculating right to left

4. Find the error in this expression:

let result = 5 + 3 * / 2;

medium

A. No error, expression is valid

B. Incorrect use of parentheses

C. Division operator should be replaced with subtraction

D. Missing operand between * and /

Solution

1. Step 1: Analyze the operator sequence

   The expression has '* /' operators together without a number between them, which is invalid syntax.

2. Step 2: Identify the syntax error

   Every operator needs operands on both sides. Here, the '*' operator is missing its right operand before the '/' operator.

3. Final Answer:

   Missing operand between * and / -> Option D

4. Quick Check:

   Operators need operands on both sides [OK]

Hint: Operators must have numbers on both sides [OK]

Common Mistakes:

• Ignoring missing operand
• Assuming expression is valid
• Confusing operator roles

5. Given the expression let x = 4 + 3 * 2 ** 2 / (1 + 1);, what is the value of x?

hard

A. 13

B. 10

C. 11

D. 14

Solution

1. Step 1: Evaluate parentheses and exponentiation first

   Parentheses: (1 + 1) = 2. Exponentiation: 2 ** 2 = 4.

2. Step 2: Calculate multiplication and division left to right

   Expression becomes 4 + 3 * 4 / 2. Calculate 3 * 4 = 12, then 12 / 2 = 6.

3. Step 3: Perform addition

   Finally, 4 + 6 = 10.

4. Final Answer:

   10 -> Option B

5. Quick Check:

   Parentheses & exponentiation first, then * /, then + [OK]

Hint: Do parentheses, then **, then * /, then + [OK]

Common Mistakes:

• Ignoring exponentiation precedence
• Doing addition before multiplication
• Miscomputing parentheses