Aptitude - Simple Interest - Discussion

Simple interest formula.

S.I=(PxRxT)/100 ---------------> (1)
where s.i =simple interest
R=rate %
P=sum or principal
T=year.


Amount = principal + simple interest
A = P + S.I ------------> (2).

From the question.
S.I = 81
Amount =450
R=4,5% P=?
A = P + S.I -----> (2)
450 = P + 81
p=450 - 81 =369 i.e :- P =369

And now using eq(1)


S.I =(P x R xT) / 100.............(1)
81=(369 x 4.5 x T) / 100
T= (81 x 100)/369 x 4.5
T= 4 years.

The amount was given but they have taken as principal. Why? Can anyone explain to me?

81 = 450 * 4.5*time/100.

81*100= 450 * 4.5 * time.
8100 = 2025 * time.
Time = 8100/2025 = 4 year.

Time = [100× S.I/P×R]yrs.
Here, from the equation
S.I = 81₹.
P. = 450₹
R. = 4.5%.
Time (T) = 100 × 81/450 × 4.5,
= 8100/2025.
=4 yrs.

450 ÷ 100 * 4.5 = 20.25.
20.25 * 4 = 81.

Can anyone explain how you got 4 years, in detail?

First, find the how much per cent 81 of 450.
(81/450)*100 = 18%.

After finding 18% then simply divide the 18% with 4.5 interest
(180/45)*100 = 4years.

In simple words, we found that 81 is the 18% of 450.
So by using 4.5 % interest p.a we need to reach 18% by 4.5 + 4.5 + 4.5 + 4.5 = 4 years.

Formulae
T= S.I *100÷P*R derives from S.I= PRT/100.
here SI is 81.
And P is 450.

Why 450 is not considered as the Principal amount?

Anyone, please explain it.

I should explain clearly in this.

Then time =100 * 81/450 * 4.5,
= 2 * 9/4.5,
= 18/4.5,
= 18 * 10/45,
= 18 * 2/9,
= 2 * 2,
= 4 years.