Simple and Compound Interest - Formulae, Concepts and Shortcuts
Today I am going to share various important questions that are repeatedly asked in bank exams. I have shared easiest way to solve these questions.
Quicker Method: Remember the following conclusion:
IMPORTANT FORMULAE
Let Principal = Rs. P, Time = t yrs and Rate = r % per annum

Solution :-
Quicker Approach:
Quicker Approach:
X becomes 2x in 4 yrs.
2x becomes 4x in next 4 yrs.
4x becomes 8x in yet another 4 yrs.
Thus, x becomes 8x in 4 + 4 + 4 = 12 yrs.


Quicker Method: Remember the following conclusion:
If a sum becomes x times in y years at CI then it will be (x)n times in ny years.
Thus, if a sum becomes 3 times in 3 years it will be (3)2 times in 2 x 3 = 6 years.
Example: If a sum deposited at compound interest becomes double in 4 years when will it be 4 times at the same rate of interest?
Solution: Using the above conclusion, we say that the sum will be (2)2 times in 2 x 4 = 8 years.
TO FIND RATE
Solution :-


GIVEN CI, To find SI and vice versa

GIVEN CI AND SI, TO FIND SUM AND RATE
Solution: A little reflection will show that the difference between the simple and compound interests for 2 yrs is the interest on the first year’s interest.
First year’s SI = Rs 40/2 = Rs 20
CI – SI = Rs 40.8 – Rs 40 = Rs 0.80
Interest on Rs 20 for 1 year = Re 0.80

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