Simple Interest and Compound Interest Tricks PDF

Today I am going to share Simple Interest and Compound Interest tricks and shortcuts.

Simple Interest 

Examples

#1

Find the simple interest, If

1. P = Rs.1000, R = 20% per annum, T = 4 years.
2. P = Rs.600, R = 5% per annum, T = 4 months.
3. P = Rs.200, R = 6% per six months, T = 3 years.
4. P = Rs.500, R = 2% per six months, T = ⁵/₂ years.
5. P = Rs.400, R = 3% per three months, T = 2 months.
6. P = Rs.730, R = 10% per annum, T = 120 days.
7. P = Rs. 3000, R = 61/4 per annum, T = period from 4th Feb to 18th Apr.

# Solution

1. 4×20×10 ⇒ 800
   
2. 2×5 = 10
   
   
   
3. 6×2×3×2 = 72 
   
4. 5×2×5=50
   
5. 4×2=8
   
6. 73/3=24
   
7. 37.50

#2 

Find the following:

1. P = Rs. 100, R = 3% per annum, T = 2 year, A= ?
2. P = Rs. 500, R = 6% per annum, T = 4 months, A= ?
3. P = Rs. 400, R = 3.65% per annum, T = 150 days, A= ?
4. A = Rs. 540, S.I = Rs. 108 , R = 5%, T = ?
5. A = Rs. 1,120, R = 5%, T = 2²/₅ yr, S.I = ?

# Solution:

1. S.I = 6 ; A = S.I + principal ; A = 6 + 100 ⇒ 106
   
2. S.I = 10 ; A = S.I + P ; A = 10+500 ⇒ 510
3. S.I = 6 ; A = 400 + 6 ⇒ 406
   
4. T = 5 yr.
   
   
   
5. 120 
   

#3 

1. A sum of money lent out at simple interest amounts to Rs. 720 after 2 years and to Rs. 1020 after a further period of 5 years. Find the sum and the rate %.
2. Adam borrowed some money at the rate of 6% p.a. for the first two years, at the rate of 9% p.a. for the next three years, and at the rate of 14% p.a. for the period beyond five years. If he pays a total interest of Rs. 11,400 at the end of nine years , how much money did he borrow ?(Bank P.O 1999)
3. A person borrows Rs. 5000 for 2 years at 4% p.a. simple interest. He immediately lends it to another person at 6¹/₄% p.a. for 2 years. Find his gain in the transaction per year.(S.S.C.2000)
4. A certain sum of money amounts to Rs. 1008 in 2 years and to Rs. 1164 in 3¹/2 years.Find the sum and the rate of interest?
5. The simple interest on a certain sum of money for 2¹/2 years at 12% per annum is Rs. 40 less than the simple interest on the same sum for 3¹/2 years at 10% per annum. Find the sum.

Practice Set For Simple Interest

Simple Interest - Problems and Answers with Detailed Explanation

P

Today I am going to share practice questions for Simple Interest. Must download read SI and CI concepts here.

1. On what sum of money lent out at 9% per annum simple interest for 6 years does the simple interest amount to Rs. 810?(RBI'82)
2. A sum of Rs. 800 amounts to Rs. 920 in 3 years at simple interest. If the interest rate is increased by 3%, it would amount to how much ?
3. A sum was put at simple interest at a certain rate for 3 years. Had it been put at 2% higher rate, it would have fetched Rs. 360 more. Find the sum.
4. The simple interest on a sum of money is 4/9 of the principal. Find the rate percent and time, if both are numerically equal.(S.S.C. 2000)
5. At what rate of interest per annum will a sum double itself in 8 years? ( Bank PO'86)
6. At what rate percent per annum will a sum of money double in 16 years? ( R.R.B. 2003)
7. A sum when reckoned at simple interest 2¹/2% per annum amounts to Rs. 630 after 2 years. Find the sum.
8. A sum of Rs. 2 is lent to be paid back in 3 equal monthly installments of Re. 1 each. Find the rate per cent .
9. What annual installment will discharge a debt of Rs. 1092 due in 3 years at 12% simple interest 
10. What annual installment will discharge a debt of Rs 4,200 due in 5 years at 10% simple interest ? (AAO '82)
11. A sum of Rs. 3,800 is lent out in two parts in such a way that the interest on one part at 8% for 5 years is equal to that on another part at ¹/₂% for 15 years. Find the sum lent out at 8%.
12. A sum of Rs. 1550 is lent out into two parts, one at 8% and another one at 6%. If the total annual income is Rs. 106, find the money lent at each rate.(L.I.C. A.A.O 2003)
13. If rs. 85 amounts to Rs. 95 in 3 years, what Rs. 102 will amount to in 5 years at the same rate percent?

# Solution 

1. 1500
r×t = ^S.I/_Principal×100 ⇒9×6 = ⁸¹⁰/P×100 ⇒ 81000/54 ⇒ 1500

2. 992
S.I = Amount - Principal ⇒S.I = 920 - 800 = 120⇒  r×t = ^S.I/_Principal×100 ⇒ r×3 = 120/800 ×100
r = 5% ⇒ Now r+3% ⇒ 5+3 = 8% ⇒  r×t = ^S.I/_Principal×100 ⇒ 8×3 = S.I/800 ×100 ⇒192
⇒ 800+192
⇒ 992

3. 6000
⇒ [^P×(R+2)×3/₁₀₀] = [^P×(R+2)×3/₁₀₀] = 360
⇒ 3PR + 6P - 3PR = 36000 ⇒ 6P = 36000 ⇒ P = 6000

4. R = 6²/₃% T= 6 yrs 8 months
⇒  r×t = ^S.I/_Principal×100 ⇒ R×R = ^4x/9/_x×100 ⇒ R² = ^400x/9
⇒ R = ²⁰/3

5. R= 12 1/2%
S.I=A-P ⇒ Let P = x ⇒SI = 2x - x ⇒ S.I = x
⇒  r×t = ^S.I/_Principal×100 ⇒ r×8= ^x/_x×100 ⇒ R = 100/8

6. R = 6¹/₄ % ( Same As Q5.)

7. P = 600
A = P + S.I
⇒ A = P + [ 1+ ^RT/₁₀₀  ]
⇒ 630 = P [ 1+ ^2×5/_100×2] ⇒630 = P × 105/108 ⇒ P = 600

8. 400%
Borrowed ( debt) amount = M, n = no. of installments , amount of equal installments = x ,
rate of percent = r (quarterly = r/4 % , monthly = r/12 % ).
M = nx [ 1 + ^r(n-1)/ ₂₀₀ ]
2 = 3×1 [ 1 + ^r(3-1)/_200×12 ]
⇒x =400 %

9. Rs.325 (Same As Q 8&10)

10. 700 per year
M = nx [ 1 + ^r(n-1)/ ₂₀₀ ]
Here, M = Rs. 4200, n = 5 , y = 1 , r  = 10% , x = annual installment = ?
4200 = 5x [ 1 + ^10×4 /₂₀₀ ]
x = Rs. 700 per year.

11. P = Rs. 600
Let the sum lent out at 8% = P₁ ; sum lent out at ¹/2 % = P₂ [since (SI)₁ = (SI)₂]
P₁ × 8×5 =P₂ × ¹/2 ×15 ⇒ P₁/P₂ = ¹⁵/_2*8*5 = ³/16
P₁ = Sum lent out at 8% = ³/₍₃₊₁₆₎ ⇒ 3800 = Rs. 600

12. 900

13. A = 122