Apply discount
- TypeScript course
- Beginner
- Lesson 74/89
- 5 min
Learn percentage discount logic.
Percentage discount
A percentage discount is applied by multiplying the amount by (1 - percent / 100). For example, a 20% discount on 100 gives 80: 100 * (1 - 20/100) = 80.
function applyDiscount(amount: number, percent: number): number {
return amount * (1 - percent / 100);
}Invalid rate check
The discount rate must be between 0 and 100. Otherwise it is safer to return the amount unchanged. This prevents accidentally applying negative or very large discounts.
function applyDiscount(amount: number, percent: number): number {
if (percent < 0 || percent > 100) {
return amount;
}
return amount * (1 - percent / 100);
}Practice Write the applyDiscount function
Write a function applyDiscount(amount: number, percent: number): number. If percent is not between 0 and 100, return amount unchanged. Otherwise return amount * (1 - percent / 100). Print three example calls: (100, 20), (50, 10), (200, 150).
Starter code
// applyDiscount(amount: number, percent: number): number yaz
// percent 0 ile 100 arasında değilse amount'u değiştirmeden döndür
// geçerliyse indirimli tutarı hesapla
// üç örneği yazdır: (100, 20), (50, 10), (200, 150)Sample solution
function applyDiscount(amount: number, percent: number): number {
if (percent < 0 || percent > 100) {
return amount;
}
return amount * (1 - percent / 100);
}
console.log(applyDiscount(100, 20));
console.log(applyDiscount(50, 10));
console.log(applyDiscount(200, 150));Expected output
80 45 200
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 What is the price of 100 units after a 20% discount?
- 100
- 20
- 80 Correct answer
- 120
Explanation: Percentage discount: amount * (1 - percent / 100). 100 * (1 - 20/100) = 100 * 0.8 = 80.
2 Complete the discount formula
return amount * (1 - ____ / 100);return amount * (1 - percent / 100);Explanation: The discount percentage is the percent variable. amount is the wrong variable; total and discount are not defined in this function.
3 Discount parts
| Term | Meaning |
|---|---|
percent / 100 |
Convert rate to decimal |
1 - percent / 100 |
Remaining rate |
amount * (1 - percent / 100) |
Discounted price |
percent < 0 || percent > 100 |
Invalid rate check |