Aptitude - Compound Interest - Discussion

Discussion Forum : Compound Interest - General Questions (Q.No. 3)
3.
There is 60% increase in an amount in 6 years at simple interest. What will be the compound interest of Rs. 12,000 after 3 years at the same rate?
Rs. 2160
Rs. 3120
Rs. 3972
Rs. 6240
None of these
Answer: Option
Explanation:

Let P = Rs. 100. Then, S.I. Rs. 60 and T = 6 years.

R = 100 x 60 = 10% p.a.
100 x 6

Now, P = Rs. 12000. T = 3 years and R = 10% p.a.

C.I.
= Rs. 12000 x 1 + 10 3 - 1
100
= Rs. 12000 x 331
1000
= 3972.

Discussion:
94 comments Page 2 of 10.

Shalini said:   1 decade ago
I'm totally confused with these problems.

When compound interest is done by individual formulas the answer shows wrong.

Poorvajain said:   1 decade ago
CI=AMT-PRINCIPLE

So in this question princple is 100 and u hve taken principle 1 why so is it wrong.

Yamini said:   1 decade ago
@Subash

There was no confusion in the given answer, here -1 is nothing but as you said Amount = {P x (1 + (R/100)^N)} - P so from this just take common as P then you get

Amount=[P x {(1 + (R/100)^N)-1}].

Dibyajyoti hazarika said:   1 decade ago
I'm confused about 331 no. How it comes?

Neha said:   1 decade ago
@dibyajyoti Hazarika.

(1+ 10/100)^3 -1
After L.C.M. it will be
{(100+10)/100}^3 -1
(110/100)^3 -1
(11/10)^3 -1 //(11x11x11=1331)and (10x10x10=1000)
(1331/1000)-1
After L.C.M.
(1331-1000)/1000
331/1000

I think now you understand about 331

Sunita Sisodiya said:   1 decade ago
Can you help with shortcut method for the same.

Sandip said:   1 decade ago
C.I = Rs. (12000*(1+(10/100)^3))-12000 = 3972.

Deepthi said:   1 decade ago
How we get S.I=Rs.60 while P=Rs.100 ?

Vicky said:   1 decade ago
Formula for C.I,

Amount = p(1+R/100)^N, Where amount = Principal + C.I.

Principal + C.I = p(1+R/100)^N.

C.I = p(1+R/100)^N - Principal, ' p ' is a common factor.

C.I = p [(1+R/100)^N-1].

Rajata said:   1 decade ago
Its totally wrong hear as compound interest 1200(1+r/1000)n.

As the given formula it should be 12000*1331/1000.

So the answer is..15972.


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