simple interest Topic-wise Short Notes, Solutions, Methods, Tips, Tricks & Techniques to Solve Problems

Simple Interest - Basic Formulas, Shortcuts, Rules, Tricks & Tips - Quantitative Aptitude

Useful For All Competitive Exams Like UPSC, SSC, BANK & RAILWAY

Posted By Careericons Team

Introduction to Simple Interest:

Interest is the sum which is paid for the use of other’s money. In other words, interest is the payment made for the money borrowed from banks or moneylenders. The money borrowed is called principal and the sum of the principal and interest is called amount.

The interest is usually paid yearly, half-yearly or quarterly as agreed upon. If it is payable yearly, it is called rate per cent per annum. For most problems involving interest, one year is taken as 365 days.

One month is taken as 30 days. When counting the number of days, the day of deposit is not counted, but the day of withdrawal is included. There are two types of interest: Simple and Compound.

When the interest on a certain sum borrowed for a certain period is reckoned uniformly, then it is called simple interest. Throughout the loan period, interest is charged on the original sum (principal) borrowed.


Important 7 Basic Formulae for solving all kinds of Simple Interest Based Aptitude Problems:

The basic formulae for calculation are as follows read one by one.

Where, Simple interest = S.I., Principal = P, Rate = R% per annum, Amount = A and Time = T years,

(i) $S.I. = {P × R × T}/100$

(ii) $P = {100 × S.I.}/{R × T}$

(iii) $R = {100 × S.I.}/{P × T}$

(iv) $T = {100 × S.I.}/{P × R}$

(v) $A = P + S.I. = P $ $(1 +{RT}/100 )$

(vi) $S.I. = A – P = {PRT}/100$

$P = {100 × S.I.}/{RT} ; R = {100 × S.I.}/ {PT} ; T = {100 × S.I.}/{RT}$

(vii) Two different cases may be compared with the formula

${A_1 - P_1}/{A_2 - P_2} = {P_1 R_1 T_1}/{P_2 R_2 T_2}$


"13" - Important Aptitude Rules, Formulas & Quick Tricks to Solve Simple Interest Based Aptitude Problems

In this list of rules, you will get an idea that How to solve all different types & kinds of Simple Interest based aptitude problems asked in various competitive exams like UPSC, SSC, Bank, and Railway examinations at all levels.

By using this method, you can able to solve all problems from basic level to advanced level of questions asked based on Simple Interest in a faster approch.

Let's discuss the rules one by one with all Simple Interest Rules & Formulas with examples,

RULE 1 :

Simple Interest (S.I.)= ${\text"Principal × Rate × Time"/100$ or

S.I. = ${\text"P × R × T"/100$

P = ${\text"S.I." × 100}/\text"R × T"$, R = ${\text"S.I." × 100}/\text"P × T"$, T = ${\text"S.I." × 100}/\text"P × R"$

A = P + S.I. or S.I. = A - P

RULE 2 :

If there are distinct rates of interest for distinct time periods i.e.

Rate for 1st $t_1$ years → $R_1$%

Rate for 2nd $t_2$ years → $R_2$%

Rate for 3rd $t_3$ years → $R_3$%. Then,

Total S.I. for 3 years = ${P(R_1t_1 + R_2t_2 + R_3t_3)}/100$

RULE 3 :

If a certain sum becomes 'n' times of itself in T years on Simple Interest, then the rate per cent per annum is.

R% = ${(n - 1)}/T × 100%$ and

T = ${(n - 1)}/R × 100%$

RULE 4 :

If a certain sum becomes $n_1$ times of itself at $R_1$% rate and $n_2$ times of itself at $R_2$% rate, then,

$R_2 = {(n_2 - 1)}/{(n_1 - 1)}R_1$ and

$T_2 = {(n_2 - 1)}/{(n_1 - 1)}T_1$

RULE 5 :

If Simple Interest (S.I.) becomes 'n' times of principal i.e.

S.I. = P × n

Then RT = n × 100

RULE 6 :

If an Amount (A) becomes 'n' times of certain sum (P) i.e.

A = Pn

Then, RT = (n – 1) × 100

RULE 7 :

If the difference between two simple interests is 'x' calculated at different annual rates and times, then principal (P) is

P = $ {x × 100}/{(\text"difference in rate") ×(\text"difference in time")}$

RULE 8 :

If a sum amounts to $x_1$ in t years and then this sum amounts to $x_2$ in t yrs. Then the sum is given by

P = $\text"(Difference in amount) × 100"/(\text"Change in interest Rate) × time"$

RULE 9 :

If a sum with simple interest rate, amounts to 'A' in $t_1$ years and 'B' in same $t_2$ years, then,

R% = ${(B - A) × 100}/{A.t_2 - B.t_1}$ and

P = ${At_2 - Bt_1}/{t_2 - t_1}$

RULE 10 :

If a sum is to be deposited in equal instalments, then,

Equal instalment = ${A × 200}/{T[200 + (T - 1)r]}$

where T = no. of years, A = amount, r = Rate of Interest.

RULE 11 :

To find the rate of interest under current deposit plan,

r = ${\text"S.I." × 2400}/{\text"n(n + 1) × (deposited amount)"}$

where n = no. of months.

RULE 12 : If certain sum P amounts to Rs. $A_1$ in $t_1$ years at rate of R% and the same sum amounts to Rs. $A_2$ in $t_2$ years at same rate of interest R%. Then,

(i) R = $({A_1 - A_2}/{A_2T_1 – A_1T_2})$ × 100

(ii) P = $({A_2T_1 – A_1T_2}/{T_1 – T_2})$

RULE 13 :

The difference between the S.I. for a certain sum $P_1$ deposited for time $T_1$ at $R_1$ rate of interest and another sum $P_2$ deposited for time $T_2$ at $R_2$ rate of interest is

S.I. = ${P_2R_2T_2 - P_1R_1T_1}/100$


6 - Types of Simple Interest Based Aptitude Questions and Answers Practise Test With Online Quiz

Click the below links & Learn the specific model from Simple Interest problems that you have to practice for upcoming examination


Refer: Get all Topic-wsie Quantitative aptitude problems for upcoming competitive exams

simple interest MCQ QUESTION & ANSWER EXERCISE
simple interest Shortcuts and Techniques with Examples

Recent Topics

Number System - Aptitude Problems For IBPS RRB PO Prelims

Free Important 100+ Aptitude Number System practice multiple choice questions and answers test & Quiz PDF for IBPS RRB PO (Officer Scale 1) Prelims 2024 Exam

29-Mar-2024 by Careericons

Continue Reading »

Classification MCQ Test: IBPS RRB PO 2024 Scale-1 Prelims

Free 150+ Classification Verbal Reasoning Multiple choice questions and answers practice test series PDF, Free Quiz For IBPS RRB PO Officer Scale 1 Level 2024

28-Mar-2024 by Careericons

Continue Reading »

100+ Analogy Verbal Questions Answers PDF For IBPS RRB PO

Most Important Analogy Verbal Reasoning Multiple choice questions and answers practice test series PDF & Free Quiz For IBPS RRB PO Officer Scale 1 Level 2024

27-Mar-2024 by Careericons

Continue Reading »

IBPS RRB Clerk 2024 Seating Arrangement Questions Answers

Seating Arrangement: Verbal Reasoning Practice multiple choice questions and answers test & Quiz PDF for IBPS RRB (Assistant Multipurpose) Clerk Prelims 2024

26-Mar-2024 by Careericons

Continue Reading »