javascriptLogic errorMediumDay 15 of 30

Going from 100 to 150 shows -50%

Time: 0:00

BugFind the bug and fix the code

What it should do

percentChange(oldValue, newValue) returns the change as a percentage of the old value. Example: percentChange(100, 150) → 50.

What happens instead

percentChange(100, 150) returns -50.

function percentChange(oldValue, newValue) {
    return ((oldValue - newValue) / oldValue) * 100;
}

Test a custom input to verify an edge case (e.g. empty lists, negative numbers, duplicates).

⏱️0:00

Hints

🏆 0 hints = Flawless Solve

Think & Test Cooldown

2:00 remaining

Take a moment to read the bug symptom and trace the code with Run & Check before unlocking Hint 1.

Hint 2

Unlocks after Hint 1

Hint 3

Unlocks after Hint 2

This bug belongs to the logic errors pattern

The wrong operator, an inverted condition, a formula the right way round but backwards.

Learn the logic errors pattern Step through your own code

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javascriptLogic errorMediumDay 15 of 30

Going from 100 to 150 shows -50%

Time: 0:00

BugFind the bug and fix the code

What it should do

percentChange(oldValue, newValue) returns the change as a percentage of the old value. Example: percentChange(100, 150) → 50.

What happens instead

percentChange(100, 150) returns -50.

function percentChange(oldValue, newValue) {
    return ((oldValue - newValue) / oldValue) * 100;
}

Test a custom input to verify an edge case (e.g. empty lists, negative numbers, duplicates).

⏱️0:00

Hints

🏆 0 hints = Flawless Solve

Think & Test Cooldown

2:00 remaining

Take a moment to read the bug symptom and trace the code with Run & Check before unlocking Hint 1.

Hint 2

Unlocks after Hint 1

Hint 3

Unlocks after Hint 2

This bug belongs to the logic errors pattern

The wrong operator, an inverted condition, a formula the right way round but backwards.

Learn the logic errors pattern Step through your own code

Going from 100 to 150 shows -50%

What it should do

What happens instead

More logic errors to practise

Related errors

Going from 100 to 150 shows -50%

What it should do

What happens instead

More logic errors to practise

Related errors