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.

Hi friends.

Here goes the explanation,

SI for 4 years = Rs 854.
SI for 3 years = Rs 815.

{4-3} = 1.

So SI for 1 year can be {854-815}.
= Rs 39.

So the SI for 3 years can be {39*3}.
= 117.

So principal is 815-117.
= RS 698{ANS}.

For four years the interest is,

854-815 = 39.
39*4 = 156.

So 854-156 = 698.

It may simple one no need to apply any formulas here. Time waste one.

Hi.

There is a simple shortcut for solving this question.

P/Sum = A1n2-A2n1/n2-n1.

= 815*4-854*3/4-3.

= 3260-2562/1 = 698.

3y---815.
4y---854.
------------
1y---39.

3y---39*3 = 117 or 4y---39*4 = 156.

815-117 = 698 or 854-156 = 698.

So we could subtract by 854 or 815.

All The best. Think smart.

Can explain me logic behind it?

Will you elaborate it in understanding way?

Sum amounts to 815 in 3 years.

Sum amounts to 854 in 4 years.

Find sum?

Let the sum be Rs. x.

x = principal amounts in 3 years = Rs. 815.

x = principal amounts in 4 years = Rs. 854.

Principal amount in 1 year = 39 I.

Interest of 1 year = Rs. 39.

Interest of 3 year = 3x39= Rs. 117.

Principal = x.
Rate = ?
Time = 3 years.
For 3 years.

Interest = Rs. 117.
Amount = Rs. 815.
Time = 3 years.

Let rate = R%.
A = p+I.
P = A-I.

= R(815-117).

Rate 698 answer.

815-p = 3*x.1 -----> equation 1.

854-p = 4*x.2 -----> equation 2.

Divide equation 1 with equation 2.

@Md Sahil.

Thank you for explaining the solution.