Aptitude - Simple Interest - Discussion

I will explain in a simple way.

We have A = P + I.

815 = P + I -----> Eq 1.

854 = P + I -----> Eq 2.

Subtract Eq 1 and 2.

Simple interest I = 815 - P - 854 + P

= 39 for 1year.

Then take for 3 years or 4 years.

You will get the same answer.

For 3 years:

39 * 3 = 117.

Or For 4 years:

39 * 4 = 156.

Then use formula A = P + I.

For 3 years:

815 = P + 117,

P = 815 - 117,

= 698.

For 4 years:

854 = P + 156,

P = 854 - 155,

= 698.

Take for 3 or 4 years answer will be same. I think the explanation is very useful.

Thanks all for explaining the answer clearly.

Hai friends,

Principle is the amount borrowed. Here, explain about SI of 3 years and 4 years. Assume P is the principal then, P+854 for 4 years and p+815 for 3yrs.

So here it is necessary to find the SI of one year and subtract it from the 3 year or 4 year.

That is, (815-117) = 698 and 854-156=698.

A sum of money at simple interest amounts to Rs. 815 in 3 years := P + SI(3 years) = 815
and to Rs. 854 in 4 years := P + SI(4 years) = 854.

p+(p*r*3)/100=815 ------> 1
p+(p*r*4)/100=854 -------> 2
on solving 1 and 2 you get := pr=3900.
put value of pr in eq-1 ,you get := p=698 (answer).

S.I. for 1 year = Rs. (854 - 815) = Rs. 39.
S.I. for 3 years = Rs.(39 x 3) = Rs. 117.
Principal = Rs. (815 - 117) = Rs. 698.

And if you want to calculate from 854
then,
SI for 4 year =Rs(39*4)=156,
Principal =Rs (854 - 156)= 698.

P = (A2 * T1 - A1 * T2)/(T1 - T2).

@Kannan.

As we say here that we have found out the interest for 3 years i.e, 117. That's why we subtracted 117 from 815.

If, we calculate the interest for 4 years..the amount will be, (39*4)= 156, then we should subtract 156 from 854, the will be same as above.

Good explanation, Thanks all.

Thanks @Appu.

Diff in SI = 854 - 815 = 39.
SI for 1 year=39 for 3 years = 39 * 3 = 117,
Then amount = 854 - 117 = 698.