Aptitude - Compound Interest - Discussion

Hi Questioners,

First if you know the how to calculate the compound intrest then it is easy. First of all calculate the compound intrest as for the given figures. If you use formula it gives the total amount with the intrest that was compunded.

After calculating the compuound intrest then half the compund intrest, that is the simple intrest of the first part of the Question then calculate the sum using the formula PTR/100=Half of the compund intrest.

Here we need to calculate the P then use the simple mathematical calculations.

You can get the answer.

Given:

Simple interest:->SI.
rate of interest = 8%.
no of years = 3 years.
p=?

SI = CI/2
Compound interest:->CI
p = 4000
rate of interest = 10%
No of years = 2

To find the principle of SI ?
First, we have to find CI,
For 1st year -> 4000*10/100 = 400 -> 4000+400 = 4400.
For 2nd year -> 4400*10/100 = 440 -> 4400+440 = 4840.

CI = 4840-4000 -> 840

then they give SI = CI/2,

SI = 840/2 -> 420
SI = P * N * R/100.
420 = p*3*8/100 -> 1750
Ans : 1750.

S.I is half of C.I
S.I = C.I/2.

For C.I, P = 4000, R = 10%, n = 2 years.
C.I = [P(1+R/100)^n] - P.
= [4000(1 + (10/100))^2] - 4000,
= 4000[(11/10)^2-1],
= 4000(21/100),
= 840.
C.I = 840.

S.I = C.I/2.
= 840/2.
= 420.
S.I = 420.

For S.I,
R=8%,
T=3 years,
P=?

S.I = PRT/100.
420 = P × 8 × 3/100.
P = 420 × 100/8 × 3.
P = 1750.

Hi,

I have answer to queries,

Here the question is tricky.

Simple interest on certain sum= 1/2 of compound interest on 4000$.

It means interest only.

Simple interest(SI)= PNR &
Compound interest(CI) = P(1+r/n)^(nt)
Its interest on certain sum = SI-P or CI-P

That's why 4000$ is deduced in equation.

See friends.

P = 4000.
R = 10.
T = 2 years.

So, C.I = P(1+r/100)^n.

C.I = 4000(110/100*110/100).

C.I = 4000(11/10*11/10).

C.I = 40*121.

C.I = 4840.

Then 4840-4840 = 840.

Given that half of the C.I i.e. 420.

= 420 = P*3*8/100 = 1750.

Hi Sandeep,

First find the C.I with the amount of Rs 4000.

Question itself mention that the amount of S.I is half the amount of C.I ......
then divide the amount of C.I by 2 and sub in S.I formula to find the principal amount....

Hi @Ishaan, Let me explain.

SI = prt.
CI = p(1+r)^n.

First we have to find CI = 4000(1+10/100)^2 = 4840.
So let me tell me why we minus 4000, Because to get the actual int
from amt 4840-4000 = 840.

@Sipun

Formula for finding CI=Amount-Principal....
find out Amount using P(1+R/100)^n then subtract with Principal getting CI.In question itself given SI is half the CI so
SI=PTR/100;
CI/2=PTR/100;

Hi @yoga,
its simple 1st we find out the C.I. on amount(4000)
later on, we half the interest on C.I. as per mention in the question and than we find out the S.I.

Hope it helps..

@Tamanna.

In question simple interest ll calculate with half of C.I. Find C.I first then so CI = 840 then we get it half so 420. Then u SI formula you'll get it.