Q.Program 5-3: Write a Python program to find the area of a rectangle given that its length is 10 units and breadth is 20 units.

Simple Interest: The Cost of Borrowing (or the Reward for Saving)

Imagine you lend a friend ₹100. A year later, they return the ₹100. You're even — but you also missed the chance to use that ₹100 yourself for a whole year. That inconvenience has a price. In finance, that price is called interest.

Simple interest is the most straightforward way to calculate that price. It says: the interest you earn (or pay) each year is a fixed percentage of the original amount you started with — no matter how many years pass.

The Core Intuition

Think of it like renting money. If you rent a car for a day, you pay a fixed daily rate. If you rent it for 5 days, you pay 5 times that daily rate. Simple interest works the same way:

• The Principal (P) is the amount you lend or borrow — the "car."
• The Rate (R) is the daily rental charge, expressed as a percentage of the car's value — the "rent per day."
• The Time (T) is how many days you keep the car — the number of years.

The total rent (interest) is just: daily rent × number of days.

The Precise Statement

Where:

• P = Principal (the original sum of money)
• R = Rate of interest per year (in percent)
• T = Time period (in years)

The Total Amount (A) you get back (or owe) at the end is:

Why Divide by 100?

The rate $R$ is given as a percentage — say 10%. "10% per year" means you get ₹10 for every ₹100 you lend, each year. So for a principal $P$, the interest for one year is:

That's the same as $\frac{P \times R}{100}$. For $T$ years, you multiply by $T$, giving $\frac{P \times R \times T}{100}$.

A Worked Example

You deposit ₹2000 in a bank that offers 8% simple interest per year. You leave it for 3 years.

• P = ₹2000
• R = 8
• T = 3

So after 3 years, you earn ₹480 in interest. Your total amount becomes:

The Key Property (and its Limitation)

Simple interest is linear — the interest grows at a constant rate each year. This makes it easy to calculate and understand. …