The word ‘Percent’ is derived from Latin word ‘per centum’ meaning ‘per hundred’. The symbol for percent is %. 
    When we take 100 as the denominator of fractions, the numerator are called percentages. Per cent can also be expressed as a ratio with its second term 100 & first term equal to the given percent.



Simple interest

Introduction to interest

Interest is the amount of money that is paid for the use of borrowed money.

Let a person 'A' borrows some money from 'B' for a certain period of fixed time at a fixed rate, then 'A' will pay the borrowed money along with the additional money, which is called interest.

 There are two types of interest:

Simple interest
Compound interest.

  • Principal
  • Amount
  • Time

Principal (P):

The money borrowed or lend out for a certain period is called the "principal" or the "sum".

Amount (A):

The sum of the interest and principal is called the amount.
Amount (A)= Principal (P)+ Interest (I).

Time (n):

The duration of the period for which the money is borrowed is called the time.
Rate Interest per Annum (r):
If interest is payable yearly for every 100 rupees, then it is called rate per cent per annum.

Introduction to simple interest

Simple interest is a quick and easy method of calculating the interest charge on loan.
Simple interest is determined by multiplying the interest rate by the principal and by the number of days that elapse between payments.
This type of interest usually applies to automobile loans or short-term loans.

Derivation of the formula to calculate the Simple interest (I):

First, take P as the principal or sum and r% as a rate percent per annum. On every ₹100 borrowed, the interest paid is ₹r.
Therefore, on ₹P borrowed, the interest paid for one year would be =P×1×r100.
Then the interest period for two years =P×2×r100.
Then the interest period for three years =P×3× r100 and so on.
If the time period is 'n ' number of years, the formula will be I=P×n×r100.

Basic Formulae:

Amount (A) :     

If the principal amount (P), and simple interest (I) are given, then we can find out the amount, by adding the principle and simple interest.

Simply rearranging both the formula as per requirement, we can find all the variants in the formula.


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clas 7 math
Medha Sharma

Course : CBSE Class 7

Start Date : 04.12.2022

End Date : 18.07.2023

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