Tips And Tricks And Shortcuts For Simple Interest Problems

July 14, 2023

Tips, Tricks & Shortcuts To Solve Simple Interest in Aptitude

To know the latest Tips and tricks and shortcuts of Simple Interest problems, go through the page entirely.

Easy Tips & Tricks, Shortcuts of Simple Interest are given below:

Tips and Tricks for Simple Interest

General Formula and Shortcuts for Simple Interest

  • Simple Interest= \mathbf{\frac{P * R * T}{100}} 
  • Simple interest is calculated by multiplying the interest rate and  principal and number of days.
  • Here, are quick and easy tips and tricks on Simple Interest problems learn easily tricks and tips on SI and efficiently in competitive exams and recruitment drive process.
  • There are mainly 2 types of questions asked in exams. However, these questions can be twisted to check the students' understanding level of the topic. 

Simple Interest Shortcut formulas.

  • If the interest on a sum of money is \frac{1}{x}of the principal, and the number of years is equal to the rate of interest then rate can be calculated using the formula: \mathbf{\sqrt{\frac{100}{x}}}
  • The rate of interest for t1 years is r1%,  t2 years is r1%,  t3 years is r3 %.  If a man gets interest of Rs x for (t1+ t2 + t3 = n)  years, then principal is given by:
    \mathbf{\frac{x*100}{r_{1}t_{1}}} + r2t2 + r3t3
  • If sum of money becomes x times in t years at simple interest, then the rate is calculated as R = \mathbf{\frac{100(x-1)}{t}} %
  • If a sum of money becomes x times in t years at simple rate of interest, then the time is calculated as t = \mathbf{\frac{100(x-1)}{R}}
  • If an amount P1 is lent out at simple interest of R1% p.a. and another amount of P2 at simple interest of R2% p.a, then the rate of interest of the whole sum is given by: R = \mathbf{\frac{P_{1}R_{1}+P_{2}R_{2}}{P_{1}+P_{2}}}

Some Tricks to Solve easily

Trick 1:-

  • If a sum of money becomes “n” times in “T years” at simple interest, then the rate
    of interest per annum can be given be
                  R=\left ( \frac{100\left ( n-1 \right )}{T} \right )

Trick 2:-

  • If an amount P1 is lent out at simple interest of R1% per annum and another
    amount P2 at simple interest rate of R2% per annum, then the rate of interest for the whole sum can be given by 
                 R=\frac{P1R1 + P2R2}{P1 + P2}

     Trick 3:-

  • A sum of money at simple interest n1 itself in t1 year. It will become n2 times of
    itself in (If Rate is constant)

                    \frac{T1}{T2}=\frac{n1-1}{n2-1}\frac{T1}{T2}=\frac{n1-1}{n2-1}

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Type 1: To find Simple Interest

Question 1. Find the simple interest of Rs 1000 for 10 years at 6% p.a.?

Options:

A. Rs. 60

B. Rs. 6000

C. Rs. 600

D. Rs. 6

Solution:    We know that,

SI = p*r*t/100

SI = 1000*6*10/100

SI = 60000/100

SI = Rs. 600

Correct option: C

Type 2: Simple Interest problem – When Rate of Interest is different for Different Years

Question 1. If a sum of Rs.25000 is given as loan for a period of 4 years with the interest rates 2%, 4%, 5%, and 6% for the 1st, 2nd, 3rd, and 4th year respectively. What is the total amount that has to be paid at the end of 4 years?

Options:

A. Rs. 29250

B. Rs. 29520

C. Rs. 25920

D. Rs. 25290

Solution:    As this is a case of Simple Interest we add 2% + 4% + 5% and 6% = 17%.

Amount = Principal + Rate of Interest.

Principal is 100% of the amount. 

Therefore,

Amount = 100% + 17%.

Therefore Amount = 117%

Amount = (117*25000)/100

=29250

Correct option: A

Type 3: Simple Interest problems To find the (Rate of Interest, Time period, Principal)

Question 1. A sum of money becomes 5 times in 20 years. Calculate the rate of interest.

Options:

A. 20%

B. 13%

C. 15%

D. 25%

Solution:    We know that, If sum of money becomes x times in t years at simple interest, then the rate is calculated as

R = 100 (x-1)/t %

R = 100 (5-1)/20 

R = 100 (4)/20

R = 400/20

R = 20%

Correct option: A

Question 2 : In an investment at 10% per annum simple interest after 2 years the interest received by Ryan is Rs. 580. What will be the principal amount that Ryan invests ?

                    Options 
                    (A) 3000 Rs

                    (B) 2000 Rs

                    (C) 2900 Rs
                   
                    (D) 2500 Rs

Solution:    S.I = \frac{P\times R\times T}{100}

580 = \frac{(P\times 10\times 2)}{100}

P = \frac{580\times 100}{10\times 2}

P = 2900 Rs

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