Question

Given that
A = 645, R = 5%( S.I) , T = 1.5 years, then the original principal P = ?​

Answer 1

Given :

Simple interest for two years = 600

Compound Interest for two years = 615

Analysis/Interpretation :

SI for first year = 300

SI for second year = 300

CI for first year = 300

CI for second year = 315

The additional CI of Rs 15 is interest on Rs 300 interest received in first year. So rate of interest is 15/300 x 100 = 5%.

Now, interest of Rs 300 at the end of first year @ 5% pa means principal at the beginning of the year is :

P = 300/5 x 100 = Rs 6000

Note that no formulae for SI or CI is used in the answer and the solution is based on understanding of core concept.

Answer 2

Answer:

simple intrest = (P*R*T)/100

645=(P*R*T)/100

Let principal = x

645=(x*5*1.5)/100

645=7.5x/100

645*100=7.5x

64500=7.5x

64500/7.5=x

8600=x

P=8600/-