Aptitude - Simple Interest - Discussion

@All.

Principle = the amt u borrowed
Interest = the small additional amount you pay for the amount you borrowed

First, let me explain to you The question.

In the question,

A sum of money at simple interest amounts to Rs. 815 in 3 years means the Principle amt together wit the interest paid for 3 yrs is Rs. 815 and similarly Principle amt together wit 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 Principle amount for a yr as Rs. 698

Brief explanation for last step:

815 = Principle amt + int for 3 yrs ---> equation 1.
117 = int for 3 yrs ---> equation 2.

Now subtract both equations, we get the principle amount.

Nice explanation. Thanks for the explanation.

Nice explanations, thanks all.

Amount(A) = Principle(p) + Simple Interest(SI).

The sum of money i.e Principle(p) invested or borrowed results an Amount of 815 in 3 years and 854 in 4 years. Since Rate of interest(R) is not mentioned assume it as same for both.

A1 = P + SI1
815 = P + SI1
P = 815 - SI1--- eq1

A2 = P + SI2
854 = P + SI2
P = 854 - SI2 ----- eq2

eq1= eq2
therefore -----> SI2 - SI1 = 854 - 815 =39
Now,
SI1 = P*T1*R/100 =P*3*R/100
SI2 = P*T2*R/100 = P*4*R/100
SI2 - SI1 = P*R/100

39 = P*R/100 -------> Here we can say T=1year, so this is SI for 1 year
now calculate SI for 3 or 4 years
SI for 1 year = 39
SI for 3 years = 39*3 = 117 Which is SI1 or SI for 4 years = 39*4 = 156 which is SI2.

A1 = P + 117
815 = P + 117
P = 815 - 117 = 698


A2 = P + 156
854 = P+156
P = 854 -156 = 698

So sum of money i.e Principle P = 698.

Anyone please explain the Formula.

Thank you @Gayatri.

815 - 854.
39.

39 * 3.
= 117.
815 - 117.
= 698.

The formula for the final amount = principle(1 + Rate × Time).

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.

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.