Aptitude - Simple Interest - Discussion

I got the answer 18, can anyone please explain?

Looking at the question,

R = sI * 100/p * T.
R * R = 432*100/ 1200,
R * R = 36,
R = 6.

@All.

The question is a little tricky.

[many years as the rate of interest] this means;
[Many years= rates of interest].

Therefore we can take anyone as a,x,t,n,r etc.

Years=rate of interest= X ----------> Eqn.(1)

We can also take the T alternative of X.

Then we solve the ans.
S.I=PTR/100.

We didn't know the value of T&R so move to the left side.
TR=(S.I * 100)/P
From Eqn. 1 we know that T&R are the same.
X*X=(S.I*100)/P.

P=principal= sum=1200.
S.I=Simple interest=432.

X^2=(432*100)/1200,
X^2=43200/1200,
X^2=432/12,
X^2=36.
X=√36.
X=6.

I am not getting this one. Please clarify the formula, clearly.

1200 * R * R/100 = 432.
12R * R = 432,
R * R = 432/12,
R * R = 36,
R = 36/2,
R = 6.

Here Amount * 100 = principle * time* rate is a simple formula for si.
432*100 = 1200*t*r.
43200/1200 = t*r.
36 = t*r.
Here t=r given;
So r=6 and t=6.

Principal = Rs.1200.
Interest = Rs.432.
Rate of interest = x%p.a.
Given the rate of interest=time duration = x.
A = P+I = Rs.1200 + Rs.432 = Rs.1632
A = P[1+(R*T/100)]
1632 = 1200[1+(x*x/100)]
1632 = 1200[1+(x^2/100)]
1632 = 1200/100(x^2+100)
1632 = 12(x^2+100)
136-100 = x^2.
36 = x^2.
x = 6.
Rate of interest = 6%p.a.

How? Please explain to me the answer.

If considered, the interest rate = 3.6%.

Then one year interest is = 1200 x 3.6% = 43.2/-.

As per the simple interest rule he paid interest for 10 years = 43.2 x 10 years = 432.

How 3.6% interest is not correct answer please explpain, because in the question there is not mention of how many years he paid interest rs. 432?

Please explain.

S.I = P * R * T/100.
1200 * R * T/100 = 432.
Let us calculate for one year;
1200 * r * 1 = 432 * 100,
r = 432 * 100/1200 * 1,
r = 6.