Mathematics is an equally important section for CTET, MPTET, KVS & DSSSB Exams and has even more abundant importance in some other exams conducted by central or state govt. Generally, there are questions asked related to basic concepts of the Simple Interest.

To let you make the most of Mathematics section, we are providing important facts related to the Simple Interest. At least 1-2 questions are asked from Simple Interest topic in most of the teaching exams. We wish you all the best of luck to come over the fear of the Mathematics section.

**How to Overcome Exam Fever, Especially When You Fear Maths**

## Simple Interest

**Simple interest** is nothing but the fixed percentage of the principal (invested/borrowed/ amount of money).

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**Principal (P):** It is the sum of money deposited/ loaned etc. also known as “Capital”.

**Interest:** It is the money paid by the borrower, calculated on the basis of Principal.

**Time (T/n):** This is the duration for which money is borrowed.

**Rate of Interest (r/R):** It is the rate at which the interest is charged on principal.

**Amount (A)** = Principal + Interest

**Some Basic Formulae : **

**Simple Interest (SI):**

P = Principal,

r = rate of interest (in %)

t = time period (yearly, half yearly etc.)

**Some Useful Short-cut Methods: **

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- If a certain sum in T years at R % per annum amounts to Rs. A, then the sum will be

- If a certain sum is invested in n types of investments in such a manner that equal amount is obtained on each investment where interest rates are R₁R₂ R₃ …..Rn respectively and time periods are T₁ T₂ T₃….. Tn respectively, then the ratio in which the amounts are invested is :

- If a certain sum of money becomes n times itself in T years at simple interest, then the rate of interest per annum is

- If a certain sum of money becomes n times itself in T years at a simple interest, then the time T in which it will become m times itself is given by

- Effect of change of P, R and T on simple interest is given by the following formulae:

Change in Simple Interest

For example, if rate (R) changes from R₁ to R₂ an P and T are fixed, then

Similarly, if principal (P) changes from P₁ to P₂ and R and T are fixed, then change in

Also, if rate (R) changes from R₁ to R₂ and time (T) changes from T₁ to T₂ but principal (P) is fixed, then change in

- If a certain sum of money P lent out at S.I. amounts to A₁ in T₁ years and to A₂ in T₂ years, then

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