Experts, Meritnation I had a doubt in of the questions I searched for the same on Meritnation - Maths - Comparing Quantities

Question

​​Experts,
Meritnation
​

I had a doubt in of the questions I searched for the same on
Meritnation I found a question exactly the same to that one There
the question was already answered by expert But, I am unable to get
into that solution properly SO, Please clarify the doubt for the
same properly Don't provide the solution that I said that I didn't
understood that

MY DOUBT WAS:
A certain sum of money amounts to RS 1344 in 3 years and RS 1440 in
5 years Find the sum and the rate of interest

The solution that the expert had provided to the question
that some other user had asked, that I am unable to understand
was:

​​​

Please my question properly with reasonable formulae and don't
provide the above solution The above solution is cofusing
{Please don't provide certified answer I want only experts
answer to any without providing any web link or certified
answer}

Shruti Tyagi · Accepted Answer

Dear student,

The alternative way of solving is

Case 1:Amount A=Rs 1344Time T=3 yearsSI=PRT100SI=P×R×3100A=P+SI⇒1344=P+3PR100⇒1344=100P+3PR100      --(1)Case 2:Amount A=Rs 1440Time T=5 yearsSI=PRT100SI=P×R×5100A=P+SI⇒1440=P+5PR100⇒1440=100P+5PR100      --(2)Subtracting (1) from (2)⇒1440-1344=100P+5PR100-100P+3PR100⇒96=100P+5PR-100P-3PR100⇒9600=2PR⇒4800=PR            --(3)Subtitutiting the value in (1)⇒1344=100P+3×4800100⇒1344=P+144⇒1344-144=P⇒P=Rs 1200from (3)4800=PR  ⇒4800=1200×R⇒48001200=R⇒R=4%
Regards