1. Find Interest Rate i = ?
Regular Deposit
(PMT Amount) C = 1000, Time n = 5 Year, Future value FV = 6715.61,
Deposit Frequency = at the beginning (Annuity Due) of every Year (1/year)
for Future value of Annuity Due method
Solution:
C=1000 (Cash flow per year)
n=5 years (Number of periods)
FV=6715.61 (Future value)
Now, Future value (Annuity Due) formula is
FV_("Annuity Due")=C*[((1+i)^n-1)/(i)]*(1+i)
:.6715.61=1000*[((1+i)^5-1)/(i)]*(1+i)
:.(6715.61)/(1000)=[((1+i)^5-1)/(i)]*(1+i)
:.[((1+i)^5-1)/(i)]*(1+i)=6.72
Now, find one solution using Newton Raphson method
Here
((1+x)^5-1)*(1+x)=6.72x:.((1+x)^5-1)(1+x)-6.72x=0Let
f(x) = ((1+x)^5-1)(1+x)-6.72xd/(dx)(((1+x)^5-1)(1+x)-6.72x)=5*(1+x)^5+((1+x)^5-1)-6.72
d/(dx)(((1+x)^5-1)(1+x)-6.72x)=d/(dx)(((1+x)^5-1)(1+x))-d/(dx)(6.72x)d/(dx)(((1+x)^5-1)(1+x))=5*(1+x)^5+((1+x)^5-1)
d/(dx)(((1+x)^5-1)(1+x))=(d/(dx)((1+x)^5-1))(1+x)+((1+x)^5-1)(d/(dx)(1+x))d/(dx)((1+x)^5-1)=5*(1+x)^4
d/(dx)((1+x)^5-1)=d/(dx)((1+x)^5)-d/(dx)(1)d/(dx)((1+x)^5)=5*(1+x)^4
d/(dx)((1+x)^5)=5*(1+x)^4*d/(dx)(1+x)d/(dx)(1+x)=1
d/(dx)(1+x)
=d/(dx)(1)+d/(dx)(x)
=0+1
=1
=5*(1+x)^4*1=5*(1+x)^4 =5*(1+x)^4-0=5*(1+x)^4 d/(dx)(1+x)=1
d/(dx)(1+x)
=d/(dx)(1)+d/(dx)(x)
=0+1
=1
=(5*(1+x)^4)(1+x)+((1+x)^5-1)*1=5*(1+x)^5+((1+x)^5-1) =(5*(1+x)^5+((1+x)^5-1))-6.72=5*(1+x)^5+((1+x)^5-1)-6.72 :. f'(x) = 5*(1+x)^5+((1+x)^5-1)-6.72x_0 = 0.11^(st) iteration :f(x_0)=f(0.1)=((1+0.1)^5-1)(1+0.1)-6.72*0.1=-0.000439f'(x_0)=f'(0.1)=5*(1+0.1)^5+((1+0.1)^5-1)-6.72=1.94306x_1 = x_0 - f(x_0)/(f'(x_0))x_1=0.1 - (-0.000439)/(1.94306)x_1=0.100226Approximate root of the equation
((1+x)^5-1)(1+x)-6.72x=0 using Newton Raphson method is
0.100226 (After 1 iterations)
n | x_0 | f(x_0) | f'(x_0) | x_1 | Update |
1 | 0.1 | -0.000439 | 1.94306 | 0.100226 | x_0 = x_1 |
:.i=0.100226
:.i=10.02 % per year
2. Find Interest Rate i = ?
Regular Deposit
(PMT Amount) C = 5000, Time n = 3 Year, Future value FV = 18205,
Deposit Frequency = at the beginning (Annuity Due) of every Year (1/year)
for Future value of Annuity Due method
Solution:
C=5000 (Cash flow per year)
n=3 years (Number of periods)
FV=18205 (Future value)
Now, Future value (Annuity Due) formula is
FV_("Annuity Due")=C*[((1+i)^n-1)/(i)]*(1+i)
:.18205=5000*[((1+i)^3-1)/(i)]*(1+i)
:.(18205)/(5000)=[((1+i)^3-1)/(i)]*(1+i)
:.[((1+i)^3-1)/(i)]*(1+i)=3.64
Now, find one solution using Newton Raphson method
Here
((1+x)^3-1)*(1+x)=3.64x:.((1+x)^3-1)(1+x)-3.64x=0Let
f(x) = ((1+x)^3-1)(1+x)-3.64xd/(dx)(((1+x)^3-1)(1+x)-3.64x)=3*(1+x)^3+((1+x)^3-1)-3.64
d/(dx)(((1+x)^3-1)(1+x)-3.64x)=d/(dx)(((1+x)^3-1)(1+x))-d/(dx)(3.64x)d/(dx)(((1+x)^3-1)(1+x))=3*(1+x)^3+((1+x)^3-1)
d/(dx)(((1+x)^3-1)(1+x))=(d/(dx)((1+x)^3-1))(1+x)+((1+x)^3-1)(d/(dx)(1+x))d/(dx)((1+x)^3-1)=3*(1+x)^2
d/(dx)((1+x)^3-1)=d/(dx)((1+x)^3)-d/(dx)(1)d/(dx)((1+x)^3)=3*(1+x)^2
d/(dx)((1+x)^3)=3*(1+x)^2*d/(dx)(1+x)d/(dx)(1+x)=1
d/(dx)(1+x)
=d/(dx)(1)+d/(dx)(x)
=0+1
=1
=3*(1+x)^2*1=3*(1+x)^2 =3*(1+x)^2-0=3*(1+x)^2 d/(dx)(1+x)=1
d/(dx)(1+x)
=d/(dx)(1)+d/(dx)(x)
=0+1
=1
=(3*(1+x)^2)(1+x)+((1+x)^3-1)*1=3*(1+x)^3+((1+x)^3-1) =(3*(1+x)^3+((1+x)^3-1))-3.64=3*(1+x)^3+((1+x)^3-1)-3.64 :. f'(x) = 3*(1+x)^3+((1+x)^3-1)-3.64x_0 = 0.11^(st) iteration :f(x_0)=f(0.1)=((1+0.1)^3-1)(1+0.1)-3.64*0.1=0.0001f'(x_0)=f'(0.1)=3*(1+0.1)^3+((1+0.1)^3-1)-3.64=0.684x_1 = x_0 - f(x_0)/(f'(x_0))x_1=0.1 - (0.0001)/(0.684)x_1=0.099854Approximate root of the equation
((1+x)^3-1)(1+x)-3.64x=0 using Newton Raphson method is
0.099854 (After 1 iterations)
n | x_0 | f(x_0) | f'(x_0) | x_1 | Update |
1 | 0.1 | 0.0001 | 0.684 | 0.099854 | x_0 = x_1 |
:.i=0.099854
:.i=9.99 % per year
This material is intended as a summary. Use your textbook for detail explanation.
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