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Aptitude - Compound Interest - Discussion

Discussion Forum : Compound Interest - General Questions (Q.No. 3)
Compound Interest
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 3 of 10.
Steve said:   1 decade ago
You make your calculation too complicated for beginners, it would have been much more easier if you just convert it to decimal and ignore the fraction thing. Good job though.
Aayushi said:   1 decade ago
Can anyone help me that why do we have to subtract the P. And when to subtract and when not to?
Sarojkumarnaik786@gmail.com said:   1 decade ago
Generally we know the formula of amount not C.I.

Amount = P(1+ R\100)^t.

If we find C.I then we should subtract the principal, then the formula changes to C.I = P((1 + R/100)^t -- 1).
Bhoomika said:   1 decade ago
What is -1 ?
Nivedita said:   1 decade ago
How you have taken P as 100 ?
Satya said:   1 decade ago
60% is equal to 60/100 i.e., S.I means adding same rate of interest every year, So here we knew that 60% is increased in 6 years, i.e., Every year it is increased by 10%.

So that 10% * 6 years= 60% for 6 years. So that rate of interest = 10%.
Satya said:   1 decade ago
@Nivedita.

Don't bother about 'P'. Think logically about r% using given data.
Josephlecocq said:   1 decade ago
Is -1 the same as p?
ANGITA said:   1 decade ago
How SI was 60?
Sandeep said:   1 decade ago
Please explain How (1+10/100)^3 is calculated?
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