Aptitude - Simple Interest - Discussion

Principal = Rs. (9800 - 3675) = Rs. 6125 ?

@Xyz

For calculationg SI for 1 year we divide it by 3 first and then we want 5yr SI, so we multiplied it by 5 got it.

Here,

A1= 9800 and T1 = 5 yrs.
A2=12005 and T2 = 8 yrs.

Formula for this type of question to find R% =( (A1-A2) / (A2*T1 - A1*T2) ) *100.
Therefore,
R% =( (9800 - 12005) / ( 12005*5 - 9800*8 ) ) * 100,
= (-2205 /-18375) * 100,
= 12%.

Why we calculate rate for 5 years?

Hi @Kashinath:

In question principle is not mention, Only S.I is mention, that's why All People are taking S.I.

We know A = P+SI

As we given,

For 5 years and for 8 years :

= 12500 = P+S.I.

= 9800 = P+S.I------->1.

On subtraction of 8 years and 5 years amount we get S.I of 3 years.

= 12500-9000 = 2205.

Then for S.I of 1 year will become = 735.

Then for 5 years it will become = 5*735 = 3675.

Form (1) we have 9800 = P+S.I.

= 9800-S.I = P.
= 9800-3675 = 6125.
=> P = 6125.

Now we calculate for are for 5 years. As we know S.I for 5 years = 3675.

And P = 6125, and T = 5.

=>3615*100/5*6125.

=>12%.

We can calculate rate for 5 years or 8 years both give the same answer.

If we calculate S. I for 5 years then we have to calculate rate for 5 years.

See S.I for 5 yrs = 5*735 = 3675.

Then principal for 5 yrs = 9800-3675 = 6125.

Then calculate rate. If we calculate S.I for 8 years then we have to calculate rate for 8 years.

S.I for 8 yrs = 8*735 = 5880.

Then principal for 8 yrs = 12005-5880 = 6125.

Then calculate rate both gives same answer.

Hope it will helpful.

A = P+I.

1) 12005 = P+5880 (Total interest for 8 years=5880).

2) P = A-I = 12005-5880 = 6125.

3) SI = PNR/100, 5880 = 6125*8*R/100.

4) So R = 5880*100/8*6125= 12.

Why difference between amount of two different years is S.I rather than amount?

I = PRT/100 -----> 735 = 6125*R*1/100 ---> R = 12%.