Aptitude - Simple Interest - Discussion

Hi Friends!

Principal = the amount you borrowed.
Interest = the small additional amount you pay for the amount you borrowed.

First let me explain you the question.
In the question,

A sum of money at simple interest amounts to Rs. 815 in 3 years means the Principal amount together with the interest paid for 3 yrs is Rs. 815 and similarly Principal amount together with the interest paid for 4 yrs is Rs. 854

Therefore, if we subtract (854-815) we get the simple interest for 1 year as Rs. 39.

Then, we calculate simple interest for 3 yrs as (39*3) = 117.

Next step, we subtract (815 - 117) to get Principal amt for a yr as Rs. 698.

Brief explanation for last step:

815 = Principal amt + int for 3 yrs ......equation 1.
117 = int for 3 yrs ......equation 2.

Now subtract both equations, we get the principal amount

I hope that this explanation will be helpful to you.

SI1 = 815.
SI2 = 854.

DIFFERENCE = SI2-SI1.
D = 854-815.
D = 39.

FOR 3 YEARS = 3*39.
= 117.

SO NOW P = 815-117.
P = 698.

In my view the interest between the 3rd & 4th year of Rs. 39/- cannot determine the same interest component for the first three years as the interest will be paid on top of the capital?

As such the interest component should reduce proportionately over the previous years?

If in this question asked rate also then how to solve this question?

If we take for four years.

39*4 = 156.

854-156 = 698 is the answer.

If we take three years.

39*3 = 117.

815-117 = 698 the answer is same !

We can do both the way.

815 ------ 854 (This value 39 increase in 1 year ).

So in four year 39*4/156.

This 156 is interest in four year.

So principle is equal to / 854-156 equal to 698.

When we apply the formula SI = PRT/100.

And when we apply the formula Amount = P+SI.

@Gayahthri explained good .

Amount for three years is 815
so AMOUNT= p + SI
A = p + pin
815= p + 3pi.......... (1)
similerly for 4 years
854 = p +4pi..........(2)
subtracting equation (1) from(2) we get
39 = pi
or
pi =39
put this value of pi in equation (1) we get
815= p+ 3*39
815= p+ 117
815-117=p
p=698

@Gayathri.

Thanks a lot dear.

Very useful answer :).