Aptitude - Compound Interest - Discussion

Thank you @P Kumar.

21% = 525 then 20% = 525/21*20 = 500 ans.

Can anybody tell me when to use this formula?

P*(1+R/100)^-P.
and when to use,
P*(1+R/100)^.

Please, explain it.

@Pratiksha,
The general formula for calculating compound interest is,
P*(1+R/100)^n, but remember to subtract off the principal after in order to get the interest,

For instance, CI =Amount - Principal.

But, in case you wish to do it at once your apply P*(1+R/100)^n - P by using this formula you automatically get the interest compounded, you may not need to subtract off the principal again like in the first case.

A farmer takes a loan of Rs:45000 at 15% per annum to instal a pump in his field. He pays back 15000 to the bank along with the interest due at the end of the first year. At the end of second year he pays back the balance to the bank. How much does the farmer pay the bank at the end of second year?

Can anyone solve this?

The amount at the end 1st year, A=45000(1+ 15/100)
= Rs 51750.

The farmer paid Rs 15000, so amount left ,A = 51750 -15000
= Rs 36750.

The amount at the end of 2nd year, A= 36750(1+ 15/100)
=Rs 42262.5.

The farmer has to Rs 42262.5 at the end of the second year.

It should be 121 instead of 21 cuz 11^2=121,
525=p(1+10/100)^2,
525=p(110/100)^2.

How get 21 in the denominator? I am not getting. Please explain me.

1+ 10/100 = 11?

Given that ;

p*21/100=525,
so P= 525*100/21,
p=2500.

Now S.I= PTR/100.
where time is doubled So T=4 and Rate is halved So R=5.
Now S.I= 2500*4*5/100.
S.I =500.